Fetch product data from market service in cart's add_to_cart route

The global add_to_cart route was calling find_or_create_cart_item without
denormalized product data, leaving NULL columns. Now fetches product info
via fetch_data("market", "products-by-ids") before creating the cart item.

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

cart/bp/cart/global_routes.py

@@ -37,13 +37,28 @@ def register(url_prefix: str) -> Blueprint:
 
     @bp.post("/add/<int:product_id>/")
     async def add_to_cart(product_id: int):
+        from shared.infrastructure.data_client import fetch_data
+
         ident = current_cart_identity()
 
+        # Fetch product data from market service (cart DB doesn't have products)
+        products_raw = await fetch_data(
+            "market", "products-by-ids",
+            params={"ids": str(product_id)},
+            required=False,
+        ) or []
+        product_data = products_raw[0] if products_raw else None
+
         cart_item = await find_or_create_cart_item(
             g.s,
             product_id,
             ident["user_id"],
             ident["session_id"],
+            product_title=product_data["title"] if product_data else None,
+            product_slug=product_data["slug"] if product_data else None,
+            product_image=product_data["image"] if product_data else None,
+            product_regular_price=product_data["regular_price"] if product_data else None,
+            product_special_price=product_data["special_price"] if product_data else None,
         )
 
         if not cart_item: