Decouple per-service Alembic migrations and fix cross-DB queries

Each service (blog, market, cart, events, federation, account) now owns
its own database schema with independent Alembic migrations. Removes the
monolithic shared/alembic/ that ran all migrations against a single DB.

- Add per-service alembic.ini, env.py, and 0001_initial.py migrations
- Add shared/db/alembic_env.py helper with table-name filtering
- Fix cross-DB FK in blog/models/snippet.py (users lives in db_account)
- Fix cart_impl.py cross-DB queries: fetch products and market_places
  via internal data endpoints instead of direct SQL joins
- Fix blog ghost_sync to fetch page_configs from cart via data endpoint
- Add products-by-ids and page-config-ensure data endpoints
- Update all entrypoint.sh to create own DB and run own migrations
- Cart now uses db_cart instead of db_market
- Add docker-compose.dev.yml, dev.sh for local development
- CI deploys both rose-ash swarm stack and rose-ash-dev compose stack
- Fix Quart namespace package crash (root_path in factory.py)

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

blog/models/snippet.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from datetime import datetime
 
-from sqlalchemy import Integer, String, Text, DateTime, ForeignKey, UniqueConstraint, Index, func
+from sqlalchemy import Integer, String, Text, DateTime, UniqueConstraint, Index, func
 from sqlalchemy.orm import Mapped, mapped_column
 
 from shared.db.base import Base
@@ -16,9 +16,7 @@ class Snippet(Base):
     )
 
     id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
-    user_id: Mapped[int] = mapped_column(
-        ForeignKey("users.id", ondelete="CASCADE"), nullable=False,
-    )
+    user_id: Mapped[int] = mapped_column(Integer, nullable=False, index=True)
     name: Mapped[str] = mapped_column(String(255), nullable=False)
     value: Mapped[str] = mapped_column(Text, nullable=False)
     visibility: Mapped[str] = mapped_column(