feat: extract shared infrastructure from shared_lib

Phase 1-3 of decoupling plan:
- Shared DB, models, infrastructure, browser, config, utils
- Event infrastructure (domain_events outbox, bus, processor)
- Structured logging
- Generic container concept (container_type/container_id)
- Alembic migrations for all schema changes

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

models/__init__.py

@@ -0,0 +1,11 @@
+from .user import User
+from .kv import KV
+from .magic_link import MagicLink
+from .menu_item import MenuItem
+
+from .ghost_membership_entities import (
+    GhostLabel, UserLabel,
+    GhostNewsletter, UserNewsletter,
+    GhostTier, GhostSubscription,
+)
+from .domain_event import DomainEvent