feat: add Getty AAT support and resolve PREMIS/BIBFRAME URIs to human-readable LOC docs

- Add Getty AAT (Art & Architecture Thesaurus) vocabulary support
  - fetchGettyAATEntity() fetches term info from vocab.getty.edu JSON-LD API
  - Extracts English labels, scope notes, and aliases
  - Shows 'concept' term type for SKOS concepts

- Add getHumanReadableUrl() to map RDF URIs to documentation pages
  - PREMIS 3.0: http://www.loc.gov/premis/rdf/v3/X → id.loc.gov HTML docs
  - BIBFRAME: http://id.loc.gov/ontologies/bibframe/X → id.loc.gov HTML docs
  - Uses c_ prefix for classes, p_ for properties

- Add Getty vocabulary prefixes (aat:, tgn:, ulan:)
- Add ontology badge colors for PREMIS 3, LOCN, Getty AAT

frontend/src/components/ontology/OntologyTermPopup.tsx

@@ -68,6 +68,11 @@ const STANDARD_PREFIXES: Record<string, string> = {
   'wikidata': 'http://www.wikidata.org/entity/',
   'wdt': 'http://www.wikidata.org/prop/direct/',
   
+  // Getty Vocabularies
+  'aat': 'http://vocab.getty.edu/aat/',
+  'tgn': 'http://vocab.getty.edu/tgn/',
+  'ulan': 'http://vocab.getty.edu/ulan/',
+  
   // Project-specific
   'linkml': 'https://w3id.org/linkml/',
   'hc': 'https://w3id.org/heritage/custodian/',
@@ -110,7 +115,7 @@ interface TermInfo {
   description?: string;
   comment?: string;
   ontologyName: string;
-  termType: 'class' | 'property' | 'individual' | 'unknown';
+  termType: 'class' | 'property' | 'individual' | 'concept' | 'unknown';
   // Class-specific
   subClassOf?: string[];
   equivalentClass?: string[];
@@ -123,6 +128,8 @@ interface TermInfo {
   // Wikidata-specific
   wikidataId?: string;
   aliases?: string[];
+  // External URL (for Getty AAT, etc.)
+  externalUrl?: string;
 }
 
 /**
@@ -134,6 +141,17 @@ interface WikidataEntity {
   aliases?: { en?: Array<{ value: string }> };
 }
 
+/**
+ * Getty AAT entity response structure (JSON-LD format)
+ */
+interface GettyAATEntity {
+  'skos:prefLabel'?: Array<{ '@value': string; '@language': string }> | { '@value': string; '@language': string };
+  'skos:altLabel'?: Array<{ '@value': string; '@language': string }>;
+  'skos:scopeNote'?: Array<{ '@value': string; '@language': string }> | { '@value': string; '@language': string };
+  'rdfs:comment'?: Array<{ '@value': string; '@language': string }> | { '@value': string; '@language': string };
+  '@type'?: string | string[];
+}
+
 /**
  * Expand a CURIE to a full URI using standard prefixes
  */
@@ -220,6 +238,107 @@ async function fetchWikidataEntity(entityId: string): Promise<TermInfo | null> {
   }
 }
 
+/**
+ * Fetch Getty AAT (Art & Architecture Thesaurus) entity information
+ */
+async function fetchGettyAATEntity(entityId: string): Promise<TermInfo | null> {
+  try {
+    // Remove aat: prefix if present
+    const id = entityId.replace(/^aat:/, '');
+    
+    const response = await fetch(
+      `http://vocab.getty.edu/aat/${id}.json`,
+      { mode: 'cors' }
+    );
+    
+    if (!response.ok) {
+      console.warn(`[OntologyTermPopup] Getty AAT fetch failed for ${id}: ${response.status}`);
+      // Return basic info with direct link as fallback
+      return {
+        uri: `http://vocab.getty.edu/aat/${id}`,
+        localName: id,
+        label: `AAT ${id}`,
+        description: 'Click to view on Getty Vocabularies',
+        ontologyName: 'Getty AAT',
+        termType: 'concept',
+        externalUrl: `http://vocab.getty.edu/aat/${id}`,
+      };
+    }
+    
+    const data = await response.json();
+    
+    // Getty returns JSON-LD, extract the main entity
+    const entity = data as GettyAATEntity;
+    
+    // Extract English label from skos:prefLabel (handles both array and single value)
+    let label = `AAT ${id}`;
+    const prefLabels = entity['skos:prefLabel'];
+    if (Array.isArray(prefLabels)) {
+      const enLabel = prefLabels.find(l => l['@language'] === 'en');
+      if (enLabel) label = enLabel['@value'];
+    } else if (prefLabels && prefLabels['@value']) {
+      label = prefLabels['@value'];
+    }
+    
+    // Extract English description from skos:scopeNote or rdfs:comment
+    let description: string | undefined;
+    const scopeNotes = entity['skos:scopeNote'];
+    if (Array.isArray(scopeNotes)) {
+      const enNote = scopeNotes.find(n => n['@language'] === 'en');
+      if (enNote) description = enNote['@value'];
+    } else if (scopeNotes && scopeNotes['@value']) {
+      description = scopeNotes['@value'];
+    }
+    
+    if (!description) {
+      const comments = entity['rdfs:comment'];
+      if (Array.isArray(comments)) {
+        const enComment = comments.find(c => c['@language'] === 'en');
+        if (enComment) description = enComment['@value'];
+      } else if (comments && comments['@value']) {
+        description = comments['@value'];
+      }
+    }
+    
+    // Extract aliases from skos:altLabel
+    const aliases: string[] = [];
+    if (entity['skos:altLabel']) {
+      const altLabels = Array.isArray(entity['skos:altLabel']) 
+        ? entity['skos:altLabel'] 
+        : [entity['skos:altLabel']];
+      altLabels.forEach(alt => {
+        if (alt['@language'] === 'en' && alt['@value']) {
+          aliases.push(alt['@value']);
+        }
+      });
+    }
+    
+    return {
+      uri: `http://vocab.getty.edu/aat/${id}`,
+      localName: id,
+      label,
+      description,
+      ontologyName: 'Getty AAT',
+      termType: 'concept',
+      aliases: aliases.length > 0 ? aliases : undefined,
+      externalUrl: `http://vocab.getty.edu/aat/${id}`,
+    };
+  } catch (error) {
+    console.error('[OntologyTermPopup] Error fetching Getty AAT entity:', error);
+    // Return basic info with link even on error
+    const id = entityId.replace(/^aat:/, '');
+    return {
+      uri: `http://vocab.getty.edu/aat/${id}`,
+      localName: id,
+      label: `AAT ${id}`,
+      description: 'Click to view on Getty Vocabularies',
+      ontologyName: 'Getty AAT',
+      termType: 'concept',
+      externalUrl: `http://vocab.getty.edu/aat/${id}`,
+    };
+  }
+}
+
 /**
  * Load term information from ontology files or Wikidata
  */
@@ -231,6 +350,11 @@ async function loadTermInfo(curie: string): Promise<TermInfo | null> {
     return fetchWikidataEntity(curie);
   }
   
+  // Handle Getty AAT terms
+  if (prefix === 'aat') {
+    return fetchGettyAATEntity(curie);
+  }
+  
   // Expand the CURIE to full URI and normalize Schema.org URIs
   let fullUri = expandCurie(curie);
   fullUri = normalizeSchemaOrgUri(fullUri);
@@ -373,6 +497,71 @@ function compactUri(uri: string): string {
   return uri;
 }
 
+/**
+ * Generate human-readable documentation URL for ontology terms.
+ * 
+ * Many ontologies have separate RDF namespace URIs and HTML documentation URLs.
+ * This function maps from the RDF URI to the human-friendly documentation page.
+ * 
+ * Supported ontologies:
+ * - PREMIS 3.0: http://www.loc.gov/premis/rdf/v3/X → https://id.loc.gov/ontologies/premis-3-0-0.html#c_X (classes) or #p_X (properties)
+ * - BIBFRAME: http://id.loc.gov/ontologies/bibframe/X → https://id.loc.gov/ontologies/bibframe.html#c_X or #p_X
+ * - Schema.org: https://schema.org/X → https://schema.org/X (same URL works)
+ * - CIDOC-CRM: http://www.cidoc-crm.org/cidoc-crm/X → https://cidoc-crm.org/Entity/X/Version-X.X.X
+ * 
+ * @param uri The RDF namespace URI
+ * @param termType Optional term type hint ('class' | 'property') for anchor generation
+ * @returns Human-readable documentation URL, or the original URI if no mapping exists
+ */
+function getHumanReadableUrl(uri: string, termType?: 'class' | 'property' | 'individual' | 'concept' | 'unknown'): string {
+  // PREMIS 3.0 Ontology
+  // RDF: http://www.loc.gov/premis/rdf/v3/RightsStatus
+  // HTML: https://id.loc.gov/ontologies/premis-3-0-0.html#c_RightsStatus
+  const premisMatch = uri.match(/^http:\/\/www\.loc\.gov\/premis\/rdf\/v3\/(.+)$/);
+  if (premisMatch) {
+    const localName = premisMatch[1];
+    // Use c_ for classes, p_ for properties
+    // If termType not provided, guess based on case: UpperCase = class, lowerCase = property
+    const prefix = termType === 'property' ? 'p_' : 
+                   termType === 'class' ? 'c_' :
+                   localName[0] === localName[0].toUpperCase() ? 'c_' : 'p_';
+    return `https://id.loc.gov/ontologies/premis-3-0-0.html#${prefix}${localName}`;
+  }
+  
+  // BIBFRAME Ontology
+  // RDF: http://id.loc.gov/ontologies/bibframe/Work
+  // HTML: https://id.loc.gov/ontologies/bibframe.html#c_Work
+  const bibframeMatch = uri.match(/^http:\/\/id\.loc\.gov\/ontologies\/bibframe\/(.+)$/);
+  if (bibframeMatch) {
+    const localName = bibframeMatch[1];
+    const prefix = termType === 'property' ? 'p_' : 
+                   termType === 'class' ? 'c_' :
+                   localName[0] === localName[0].toUpperCase() ? 'c_' : 'p_';
+    return `https://id.loc.gov/ontologies/bibframe.html#${prefix}${localName}`;
+  }
+  
+  // CIDOC-CRM (direct link to class page)
+  // RDF: http://www.cidoc-crm.org/cidoc-crm/E27_Site
+  // HTML: https://cidoc-crm.org/Entity/E27-Site/version-7.1.3 (complex, just use search)
+  // For now, link to the main CIDOC-CRM website with the entity name
+  const cidocMatch = uri.match(/^http:\/\/www\.cidoc-crm\.org\/cidoc-crm\/(.+)$/);
+  if (cidocMatch) {
+    // CIDOC-CRM's HTML pages are complex, so link to their entity search
+    // They don't have simple anchors, so we'll use the RDF URI which redirects
+    return uri;
+  }
+  
+  // RiC-O (Records in Contexts Ontology)
+  // RDF: https://www.ica.org/standards/RiC/ontology#Rule
+  // HTML: https://www.ica.org/standards/RiC/ontology (no anchors, but URI works as-is)
+  
+  // Schema.org - URI works as-is (content negotiation)
+  // https://schema.org/name → works for both RDF and HTML
+  
+  // Default: return original URI
+  return uri;
+}
+
 /**
  * Ontology badge colors based on the ontology type
  */
@@ -389,13 +578,18 @@ const ONTOLOGY_COLORS: Record<string, string> = {
   'DCAT 3': '#3B82F6',             // Blue
   'CPOV (Core Public Org)': '#3B82F6',
   'BIBFRAME': '#14B8A6',           // Teal
+  'PREMIS 3': '#0891B2',           // Cyan - LOC digital preservation
   'EDM': '#0369A1',                // Sky dark - Europeana blue
   'TOOI': '#14B8A6',
   'PiCo': '#0EA5E9',               // Sky
   'Wikidata': '#339966',           // Wikidata green
+  'Getty AAT': '#990033',          // Getty maroon
+  'Getty TGN': '#990033',          // Getty maroon
+  'Getty ULAN': '#990033',         // Getty maroon
   'TIME': '#6B7280',               // Gray
   'GEO': '#059669',                // Emerald
   'VCard': '#7C3AED',              // Violet
+  'LOCN': '#7C3AED',               // Violet - W3C location
 };
 
 export const OntologyTermPopup: React.FC<OntologyTermPopupProps> = ({
@@ -621,18 +815,19 @@ export const OntologyTermPopup: React.FC<OntologyTermPopupProps> = ({
     };
   }, [isResizing, handleResizeMouseMove, handleResizeMouseUp, isDragging]);
 
-  // Render URI as clickable link
+  // Render URI as clickable link with human-readable documentation URL
-  const renderUri = (uri: string) => {
+  const renderUri = (uri: string, termType?: 'class' | 'property' | 'individual' | 'concept' | 'unknown') => {
     const compact = compactUri(uri);
+    const humanReadableUrl = getHumanReadableUrl(uri, termType);
     return (
       <span className="ontology-popup__uri">
         <code className="ontology-popup__uri-compact">{compact}</code>
         <a 
-          href={uri} 
+          href={humanReadableUrl} 
           target="_blank" 
           rel="noopener noreferrer"
           className="ontology-popup__uri-link"
-          title={uri}
+          title={humanReadableUrl !== uri ? `${humanReadableUrl}\n(RDF: ${uri})` : uri}
         >
           ↗
         </a>
@@ -745,9 +940,23 @@ export const OntologyTermPopup: React.FC<OntologyTermPopupProps> = ({
               {/* URI */}
               <div className="ontology-popup__section">
                 <span className="ontology-popup__section-label">URI:</span>
-                {renderUri(termInfo.uri)}
+                {renderUri(termInfo.uri, termInfo.termType)}
               </div>
               
+              {/* External link for Getty AAT and similar external vocabularies */}
+              {termInfo.externalUrl && (
+                <div className="ontology-popup__section">
+                  <a 
+                    href={termInfo.externalUrl}
+                    target="_blank"
+                    rel="noopener noreferrer"
+                    className="ontology-popup__external-link"
+                  >
+                    View on {termInfo.ontologyName} →
+                  </a>
+                </div>
+              )}
+              
               {/* Description / Comment */}
               {(termInfo.description || termInfo.comment) && (
                 <div className="ontology-popup__section">
@@ -779,7 +988,7 @@ export const OntologyTermPopup: React.FC<OntologyTermPopupProps> = ({
                   <span className="ontology-popup__section-label">Subclass of:</span>
                   <div className="ontology-popup__uri-list">
                     {termInfo.subClassOf.map((uri, idx) => (
-                      <div key={idx}>{renderUri(uri)}</div>
+                      <div key={idx}>{renderUri(uri, 'class')}</div>
                     ))}
                   </div>
                 </div>
@@ -791,7 +1000,7 @@ export const OntologyTermPopup: React.FC<OntologyTermPopupProps> = ({
                   <span className="ontology-popup__section-label">Domain:</span>
                   <div className="ontology-popup__uri-list">
                     {termInfo.domain.map((uri, idx) => (
-                      <div key={idx}>{renderUri(uri)}</div>
+                      <div key={idx}>{renderUri(uri, 'class')}</div>
                     ))}
                   </div>
                 </div>
@@ -802,7 +1011,7 @@ export const OntologyTermPopup: React.FC<OntologyTermPopupProps> = ({
                   <span className="ontology-popup__section-label">Range:</span>
                   <div className="ontology-popup__uri-list">
                     {termInfo.range.map((uri, idx) => (
-                      <div key={idx}>{renderUri(uri)}</div>
+                      <div key={idx}>{renderUri(uri, 'class')}</div>
                     ))}
                   </div>
                 </div>
@@ -820,7 +1029,7 @@ export const OntologyTermPopup: React.FC<OntologyTermPopupProps> = ({
               {termInfo.inverseOf && (
                 <div className="ontology-popup__section">
                   <span className="ontology-popup__section-label">Inverse of:</span>
-                  {renderUri(termInfo.inverseOf)}
+                  {renderUri(termInfo.inverseOf, 'property')}
                 </div>
               )}
               
@@ -830,7 +1039,7 @@ export const OntologyTermPopup: React.FC<OntologyTermPopupProps> = ({
                   <span className="ontology-popup__section-label">Sub-property of:</span>
                   <div className="ontology-popup__uri-list">
                     {termInfo.subPropertyOf.map((uri, idx) => (
-                      <div key={idx}>{renderUri(uri)}</div>
+                      <div key={idx}>{renderUri(uri, 'property')}</div>
                     ))}
                   </div>
                 </div>