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>

CLAUDE.md

@@ -2,6 +2,10 @@
 
 Federated content-addressed DAG execution engine for distributed media processing with ActivityPub ownership and provenance tracking.
 
+## Deployment
+
+- **Do NOT push** until explicitly told to. Pushes reload code to dev automatically.
+
 ## Project Structure
 
 ```
@@ -54,6 +58,9 @@ docker build -f l2/Dockerfile -t l2-server:latest .
 - **Celery Tasks**: In `l1/tasks/`, decorated with `@app.task`
 - **S-Expression Effects**: Composable effect language in `l1/sexp_effects/`
 - **Storage**: Local filesystem, S3, or IPFS backends (`storage_providers.py`)
+- **Inter-Service Reads**: `fetch_data()` → GET `/internal/data/{query}` (HMAC-signed)
+- **Inter-Service Actions**: `call_action()` → POST `/internal/actions/{name}` (HMAC-signed)
+- **Inter-Service AP Inbox**: `send_internal_activity()` → POST `/internal/inbox` (HMAC-signed, AP-shaped activities for cross-service writes with denormalized data)
 
 ## Auth