Use id+slug paths for user products and count their visits.

Align storefront/sitemap URLs with catalog products, add by-id public APIs, and include user-product detail views in the product visit chart.

Co-authored-by: Cursor <cursoragent@cursor.com>

database/migrations/092_website_page_kind_user_products.sql

@@ -0,0 +1,4 @@
+-- Track public customer marketplace (user product) list/detail page views.
+
+ALTER TYPE website_page_kind ADD VALUE IF NOT EXISTS 'user_product_list';
+ALTER TYPE website_page_kind ADD VALUE IF NOT EXISTS 'user_product_detail';