prices: fold groceries and CS skins into one price tracker (/trackers/prices) with tabs

- tab registry in #lib/price-trackers (add a tab = route + entry + icon)
- groceries -> /trackers/prices/groceries (owner-only), CS prices -> /trackers/prices/cs (public)
- old /trackers/groceries/* and /projects/cs-prices/* redirect (301 GET, 308 POST) with query
- nav: one prices entry replaces groceries and skins; cyan price-tag icon

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

@@ -32,6 +32,7 @@ const staticPaths = [
 	'/trackers/books',
 	'/trackers/ai',
 	'/trackers/radio',
+	'/trackers/prices/cs',
 	'/trackers/spotting',
 	'/trackers/cars',
 	'/trackers/cars/brands',