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/order/routes.py

@@ -5,7 +5,6 @@ from sqlalchemy import select, func, or_, cast, String, exists
 from sqlalchemy.orm import selectinload
 
 
-from shared.models.market import Product
 from shared.models.order import Order, OrderItem
 from shared.browser.app.payments.sumup import create_checkout as sumup_create_checkout
 from shared.config import config
@@ -49,7 +48,7 @@ def register() -> Blueprint:
         result = await g.s.execute(
             select(Order)
             .options(
-                selectinload(Order.items).selectinload(OrderItem.product)
+                selectinload(Order.items)
             )
             .where(Order.id == order_id, owner)
         )