Add requirements.txt and guard app model imports in env.py

requirements.txt copied from shared_lib for Docker build compatibility.
Alembic env.py now uses try/except for app-specific model imports so
upgrade head works in Docker where only one app's code is present.

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

alembic/env.py

@@ -19,10 +19,11 @@ from shared.db.base import Base
 
 # Import ALL models so Base.metadata sees every table
 import shared.models  # noqa: F401  User, KV, MagicLink, MenuItem, Ghost*
-import blog.models  # noqa: F401  Post, Author, Tag, Snippet, TagGroup
-import market.models  # noqa: F401  Product, CartItem, MarketPlace, etc.
-import cart.models  # noqa: F401  Order, OrderItem, PageConfig
-import events.models  # noqa: F401  Calendar, CalendarEntry, Ticket, etc.
+for _mod in ("blog.models", "market.models", "cart.models", "events.models"):
+    try:
+        __import__(_mod)
+    except ImportError:
+        pass  # OK in Docker — only needed for autogenerate
 
 target_metadata = Base.metadata