Decouple cart/market DBs: denormalize product data, AP internal inbox, OAuth scraper auth

Remove cross-DB relationships (CartItem.product, CartItem.market_place,
OrderItem.product) that break with per-service databases. Denormalize
product and marketplace fields onto cart_items/order_items at write time.

- Add AP internal inbox infrastructure (shared/infrastructure/internal_inbox*)
  for synchronous inter-service writes via HMAC-authenticated POST
- Cart inbox blueprint handles Add/Remove/Update rose:CartItem activities
- Market app sends AP activities to cart inbox instead of writing CartItem directly
- Cart services use denormalized columns instead of cross-DB hydration/joins
- Add marketplaces-by-ids data endpoint to market service
- Alembic migration adds denormalized columns to cart_items and order_items
- Add OAuth device flow auth to market scraper persist_api (artdag client pattern)

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

cart/bp/cart/services/get_cart.py

@@ -1,25 +1,55 @@
+from types import SimpleNamespace
+
 from sqlalchemy import select
-from sqlalchemy.orm import selectinload
 
 from shared.models.market import CartItem
 from .identity import current_cart_identity
 
-async def get_cart(session):
-  ident = current_cart_identity()
-  
-  filters = [CartItem.deleted_at.is_(None)]
-  if ident["user_id"] is not None:
-      filters.append(CartItem.user_id == ident["user_id"])
-  else:
-      filters.append(CartItem.session_id == ident["session_id"])
 
-  result = await session.execute(
-      select(CartItem)
-      .where(*filters)
-      .order_by(CartItem.created_at.desc())
-      .options(
-          selectinload(CartItem.product),
-          selectinload(CartItem.market_place),
-      )
-  )
-  return result.scalars().all()
+def _attach_product_namespace(ci: CartItem) -> None:
+    """Build a SimpleNamespace 'product' from denormalized columns for template compat."""
+    ci.product = SimpleNamespace(
+        id=ci.product_id,
+        title=ci.product_title,
+        slug=ci.product_slug,
+        image=ci.product_image,
+        brand=ci.product_brand,
+        regular_price=ci.product_regular_price,
+        special_price=ci.product_special_price,
+        regular_price_currency=ci.product_price_currency,
+    )
+
+
+def _attach_market_place_namespace(ci: CartItem) -> None:
+    """Build a SimpleNamespace 'market_place' from denormalized columns."""
+    if ci.market_place_id:
+        ci.market_place = SimpleNamespace(
+            id=ci.market_place_id,
+            name=ci.market_place_name,
+            container_id=ci.market_place_container_id,
+        )
+    else:
+        ci.market_place = None
+
+
+async def get_cart(session):
+    ident = current_cart_identity()
+
+    filters = [CartItem.deleted_at.is_(None)]
+    if ident["user_id"] is not None:
+        filters.append(CartItem.user_id == ident["user_id"])
+    else:
+        filters.append(CartItem.session_id == ident["session_id"])
+
+    result = await session.execute(
+        select(CartItem)
+        .where(*filters)
+        .order_by(CartItem.created_at.desc())
+    )
+    items = list(result.scalars().all())
+
+    for ci in items:
+        _attach_product_namespace(ci)
+        _attach_market_place_namespace(ci)
+
+    return items