Skip resolve_product redirects for POST requests (cart, like)

resolve_product's canonical slug redirect causes a 302 loop on POST
/cart/ because it redirects to the GET product detail page. POST
endpoints only need g.product_slug to look up the product — skip
the full resolution/redirect logic.

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

bp/product/routes.py

@@ -34,10 +34,16 @@ def register():
     # ─────────────────────────────────────────────────────────────
     @bp.before_request
     async def resolve_product():
+        from quart import request as req
+
         raw_slug = g.product_slug = getattr(g, "product_slug", None)
         if raw_slug is None:
             return
 
+        # POST endpoints (cart, like) only need the slug — skip redirects
+        if req.method == "POST":
+            return
+
         # 1. If slug is INT → load product by ID
         if raw_slug.isdigit():
             product_id = int(raw_slug)