stats: /stats overview, economy, energy and Gouda pages; CBS series map; nav, homepage, /start and sitemap links

- CBS_SERIES: CPI, household tariffs (2007-now), energy balance, renewables, heat pumps,
  solar, cars, population (monthly, since 1942, components), house prices, housing stock,
  municipal levies for Gouda and its neighbours
- shared StatChart/Kpi/chart helpers with per-chart source attribution
- drop Eurostat nrg_pc_20x_h (404; CBS covers that history)

src/routes/sitemap.xml/+server.ts

@@ -14,6 +14,10 @@ const staticPaths = [
 	'/trackers',
 	'/blog',
 	'/lists',
+	'/stats',
+	'/stats/economy',
+	'/stats/energy',
+	'/stats/gouda',
 	'/trackers/books',
 	'/trackers/spotting',
 	'/trackers/cars',