feat(transform): add three pSEO serving models — city costs, country overview, city pricing

- pseo_city_costs_de: unblocks city-cost-de template (~600 city pages),
  joins city_market_profile + planner_defaults, includes camelCase calc
  override columns (ratePeak, rateOffPeak, utilTarget, dblCourts, country)
- pseo_country_overview: per-country hub aggregating from pseo_city_costs_de,
  includes top_city_slugs/names lists for internal linking
- pseo_city_pricing: per-city pricing pages requiring >= 2 Playtomic venues,
  includes P25/P75 price range and occupancy

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

transform/sqlmesh_padelnomics/models/serving/pseo_country_overview.sql

@@ -0,0 +1,37 @@
+-- pSEO article data: per-country padel market overview.
+-- One row per country — consumed by the country-overview.md.jinja template.
+-- Aggregates city-level data from pseo_city_costs_de.
+--
+-- top_city_slugs / top_city_names are ordered lists (up to 5) used to generate
+-- internal links from the country hub to its top city pages.
+
+MODEL (
+  name serving.pseo_country_overview,
+  kind FULL,
+  cron '@daily',
+  grain country_slug
+);
+
+SELECT
+  country_code,
+  country_name_en,
+  country_slug,
+  COUNT(*)                                                        AS city_count,
+  SUM(padel_venue_count)                                         AS total_venues,
+  ROUND(AVG(market_score), 1)                                    AS avg_market_score,
+  MAX(market_score)                                              AS top_city_market_score,
+  -- Top 5 cities by market score for internal linking (DuckDB list slice syntax)
+  LIST(city_slug ORDER BY market_score DESC NULLS LAST)[1:5]     AS top_city_slugs,
+  LIST(city_name ORDER BY market_score DESC NULLS LAST)[1:5]     AS top_city_names,
+  -- Pricing medians across cities (NULL when no Playtomic coverage in country)
+  ROUND(MEDIAN(median_hourly_rate), 0)                           AS median_hourly_rate,
+  ROUND(MEDIAN(median_peak_rate), 0)                             AS median_peak_rate,
+  ROUND(MEDIAN(median_offpeak_rate), 0)                          AS median_offpeak_rate,
+  -- Use the most common currency in the country (MIN is deterministic for single-currency countries)
+  MIN(price_currency)                                            AS price_currency,
+  SUM(population)                                                AS total_population,
+  CURRENT_DATE                                                   AS refreshed_date
+FROM serving.pseo_city_costs_de
+GROUP BY country_code, country_name_en, country_slug
+-- Only countries with enough cities to be worth a hub page
+HAVING COUNT(*) >= 2