feat(rag): add database routing to 8 more factual query templates

Add databases: ["oxigraph"] to skip vector search for deterministic queries:
- count_institutions_by_type_location (count)
- count_institutions_by_type (aggregation)
- find_institutions_by_founding_date (temporal)
- find_custodians_by_budget_threshold (financial)
- compare_locations (comparative)
- find_by_founding (temporal)
- events_in_period (temporal events)
- institutions_by_founding_decade (temporal aggregation)

Total templates with oxigraph-only routing: 12

data/sparql_templates.yaml

@@ -1433,6 +1433,7 @@ templates:
     description: "Find organizational change events in a time period"
     intent: ["temporal", "statistical"]
     response_modes: ["table", "chart"]
+    databases: ["oxigraph"]  # Temporal event query - Oxigraph only, skip vector search
     ui_template:
       nl: "Gevonden: {{ result_count }} gebeurtenissen tussen {{ start_date }} en {{ end_date }}."
       en: "Found: {{ result_count }} events between {{ start_date }} and {{ end_date }}."
@@ -1613,6 +1614,7 @@ templates:
     description: "Count or list institutions by founding decade"
     intent: ["temporal", "statistical"]
     response_modes: ["table", "chart"]
+    databases: ["oxigraph"]  # Temporal aggregation - Oxigraph only, skip vector search
     ui_template:
       nl: "Verdeling van {{ institution_type_nl }} per decennium:"
       en: "Distribution of {{ institution_type_en }} by decade:"