feat: persist customer product and shop favorites through the live API

Replace mall fixture favorites with customer-scoped endpoints, and send signed-out shoppers back to the page they left after sign-in.

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

apps/api/src/modules/mod.rs

@@ -6,6 +6,7 @@ pub mod catalog;
 pub mod content;
 pub mod coupon;
 pub mod currency;
+pub mod favorite;
 pub mod flash_sale;
 pub mod fulfillment;
 pub mod group_buying;
@@ -30,6 +31,7 @@ pub fn api_router() -> Router<AppState> {
         .merge(content::router())
         .merge(cart::router())
         .merge(coupon::router())
+        .merge(favorite::router())
         .merge(flash_sale::router())
         .merge(group_buying::router())
         .merge(order::router())