Fix cross-DB query: market app cart_items via data endpoint

market_context() was querying CartItem directly via g.s (db_market),
but cart_items lives in db_cart. Replace with fetch_data("cart",
"cart-items") and add the corresponding data endpoint.

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

cart/bp/data/routes.py

@@ -80,4 +80,36 @@ def register() -> Blueprint:
 
     _handlers["page-config-ensure"] = _page_config_ensure
 
+    # --- cart-items (product slugs + quantities for template rendering) ---
+    async def _cart_items():
+        from sqlalchemy import select
+        from sqlalchemy.orm import selectinload
+        from shared.models.market import CartItem
+
+        user_id = request.args.get("user_id", type=int)
+        session_id = request.args.get("session_id")
+
+        filters = [CartItem.deleted_at.is_(None)]
+        if user_id is not None:
+            filters.append(CartItem.user_id == user_id)
+        elif session_id is not None:
+            filters.append(CartItem.session_id == session_id)
+        else:
+            return []
+
+        result = await g.s.execute(
+            select(CartItem).where(*filters).options(selectinload(CartItem.product))
+        )
+        items = result.scalars().all()
+        return [
+            {
+                "product_id": item.product_id,
+                "product_slug": item.product.slug if item.product else None,
+                "quantity": item.quantity,
+            }
+            for item in items
+        ]
+
+    _handlers["cart-items"] = _cart_items
+
     return bp