Add companion_query support to fetch full entity records alongside
aggregate count queries. Enables displaying results on map/list when
asking 'how many museums in Amsterdam?'
Backend changes:
- Add companion_query, companion_query_region, companion_query_country
fields to TemplateDefinition and TemplateMatchResult
- Add render_template_string() for raw companion query rendering
Template changes:
- Add companion queries to count_institutions_by_type_and_location
for settlement, region, and country level queries
- Returns institution URI, name, coordinates, city for visualization
