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/alembic/versions/005_create_notifications.py

@@ -0,0 +1,39 @@
+"""Create notifications table
+
+Revision ID: 005
+Revises: 004
+Create Date: 2026-03-19
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+revision: str = "005"
+down_revision: Union[str, None] = "004"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "notifications",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True, server_default=sa.text("gen_random_uuid()")),
+        sa.Column("user_id", UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True),
+        sa.Column("title", sa.String(255), nullable=False),
+        sa.Column("body", sa.Text, nullable=False),
+        sa.Column("type", sa.String(30), nullable=False, server_default="info"),
+        sa.Column("channel", sa.String(20), nullable=False, server_default="in_app"),
+        sa.Column("status", sa.String(20), nullable=False, server_default="pending"),
+        sa.Column("scheduled_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("sent_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("read_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("metadata", JSONB, nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("notifications")