feat(sql): thread opportunity_score from location_opportunity_profile into pSEO serving chain

- dim_cities: add geoname_id to geonames_pop CTE and final SELECT
  Creates FK between dim_cities (city-with-padel-venues) and dim_locations (all GeoNames),
  enabling joins to location_opportunity_profile for the first time.
- city_market_profile: pass geoname_id through base CTE and final SELECT
- pseo_city_costs_de: LEFT JOIN location_opportunity_profile on (country_code, geoname_id),
  add opportunity_score to output columns
- pseo_country_overview: add avg_opportunity_score, top_opportunity_score, top_opportunity_slugs,
  top_opportunity_names aggregates

Cities with no GeoNames name match get opportunity_score = NULL; templates guard with
{% if opportunity_score %}.

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

transform/sqlmesh_padelnomics/models/foundation/dim_cities.sql

@@ -75,7 +75,7 @@ uk_pop AS (
 ),
 -- GeoNames global fallback (all cities ≥50K)
 geonames_pop AS (
-  SELECT city_name, country_code, population, ref_year
+  SELECT geoname_id, city_name, country_code, population, ref_year
   FROM staging.stg_population_geonames
   QUALIFY ROW_NUMBER() OVER (PARTITION BY geoname_id ORDER BY ref_year DESC) = 1
 )
@@ -153,7 +153,10 @@ SELECT
   )::INTEGER                                                 AS population_year,
   vc.padel_venue_count,
   ci.median_income_pps,
-  ci.income_year
+  ci.income_year,
+  -- GeoNames ID: FK to dim_locations / location_opportunity_profile.
+  -- NULL when city name doesn't match any GeoNames entry.
+  gn.geoname_id
 FROM venue_cities vc
 LEFT JOIN country_income ci ON vc.country_code = ci.country_code
 -- Eurostat EU population (via city code→name lookup)