feat(notifications): add per-user notification system with inbox, email, and webhook targets

- Add UserNotificationTarget, UserNotificationPreference, InAppNotification models
- Add migration 025_add_user_notifications (tables + indexes)
- Add app/utils/user_notification.py dispatch service
- Add app/api/notifications.py REST endpoints (inbox, targets, preferences)
- Add app/views/notifications.py view route
- Add frontend/templates/notifications_dashboard.html Alpine.js dashboard
- Add bell icon with unread badge in base.html nav (desktop + mobile)
- Register routers in app/api/__init__.py and app/views/__init__.py
- Add 32 unit tests in tests/test_notifications_api.py

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

app/views/__init__.py

@@ -18,6 +18,7 @@ from app.views.help import router as help_router  # Built-in help / How-To docs
 from app.views.imap_accounts import router as imap_accounts_router
 from app.views.integrations import router as integrations_router  # Unified integrations dashboard
 from app.views.license_routes import router as license_router  # Add the license router
+from app.views.notifications import router as notifications_router
 from app.views.onboarding import router as onboarding_router
 from app.views.onedrive import router as onedrive_router
 from app.views.pipelines import router as pipelines_router  # Processing pipelines
@@ -52,4 +53,5 @@ router.include_router(onboarding_router)  # User onboarding wizard
 router.include_router(pipelines_router)  # Processing pipelines
 router.include_router(imap_accounts_router)  # Per-user IMAP ingestion accounts
 router.include_router(integrations_router)  # Unified integrations dashboard
+router.include_router(notifications_router)  # User notification dashboard
 router.include_router(help_router)  # Built-in help / How-To docs