feat(maps): Phase 4 — city venue dot map

New serving model: city_venue_locations joins dim_venues + dim_cities
to expose lat/lon/court_count per venue for the city dot map endpoint.

pseo_city_costs_de.sql: add c.lat, c.lon so city-cost articles have
city coordinates for the #city-map data attributes.

city-cost-de.md.jinja: add #city-map div (both DE and EN sections)
after the stats strip. Leaflet init handled by article_detail.html.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

transform/sqlmesh_padelnomics/models/serving/city_venue_locations.sql

@@ -0,0 +1,26 @@
+-- Per-venue lat/lon for the city detail dot map.
+-- Joins dim_venues to dim_cities to attach country_slug and city_slug
+-- (needed by the /api/markets/<country>/<city>/venues.json endpoint).
+-- Only rows with valid coordinates are included.
+
+MODEL (
+  name serving.city_venue_locations,
+  kind FULL,
+  cron '@daily',
+  grain venue_id
+);
+
+SELECT
+  v.venue_id,
+  v.name,
+  v.lat,
+  v.lon,
+  v.court_count,
+  v.indoor_court_count,
+  v.outdoor_court_count,
+  v.city_slug,
+  c.country_slug
+FROM foundation.dim_venues v
+JOIN foundation.dim_cities c
+  ON v.country_code = c.country_code AND v.city_slug = c.city_slug
+WHERE v.lat IS NOT NULL AND v.lon IS NOT NULL

transform/sqlmesh_padelnomics/models/serving/pseo_city_costs_de.sql

@@ -22,6 +22,9 @@ SELECT
   c.country_code,
   c.country_name_en,
   c.country_slug,
+  -- City coordinates (for the city venue dot map)
+  c.lat,
+  c.lon,
   -- Market metrics
   c.population,
   c.padel_venue_count,