Phase 5: Notifications — WebSocket, APScheduler, AI tool, health review

Backend:
- Notification model + Alembic migration
- Notification service: CRUD, mark read, unread count, pending scheduled
- WebSocket manager singleton for real-time push
- WebSocket endpoint /ws/notifications with JWT auth via query param
- APScheduler integration: periodic notification sender (every 60s),
  daily proactive health review job (8 AM)
- AI tool: schedule_notification (immediate or scheduled)
- Health review worker: analyzes user memory via Claude, creates
  ai_generated notifications with WebSocket push

Frontend:
- Notification API client + Zustand store
- WebSocket hook with auto-reconnect (exponential backoff)
- Notification bell in header with unread count badge + dropdown
- Notifications page with type badges, mark read, mark all read
- WebSocket initialized in AppLayout for app-wide real-time updates
- Enabled notifications nav in sidebar
- English + Russian translations

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/models/user.py

@@ -29,3 +29,4 @@ class User(Base):
     skills: Mapped[list["Skill"]] = relationship(back_populates="user", cascade="all, delete-orphan")  # noqa: F821
     documents: Mapped[list["Document"]] = relationship(back_populates="user", cascade="all, delete-orphan")  # noqa: F821
     memory_entries: Mapped[list["MemoryEntry"]] = relationship(back_populates="user", cascade="all, delete-orphan")  # noqa: F821
+    notifications: Mapped[list["Notification"]] = relationship(back_populates="user", cascade="all, delete-orphan")  # noqa: F821