feat: web push notifications (VAPID)

- push_utils.py: subscription storage + send helper (auto-prunes 410 endpoints)
- routers/push.py: GET /api/push/vapid-key (public), POST/DELETE /api/push/subscribe
- sw.js: push event listener shows notification; notificationclick focuses/opens tab
- app.js: subscribe/unsubscribe flow + "Enable notifications" toggle in settings dropdown
- tools/notify.py: web_push orchestrator tool (user-level, no admin required)
- VAPID keys in .env; pywebpush added to requirements.txt

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

cortex/main.py

@@ -9,7 +9,7 @@ logging.basicConfig(level=logging.INFO, format="%(levelname)s:%(name)s: %(messag
 from config import settings
 from auth_middleware import SessionAuthMiddleware
 from routers import chat, google_chat, nextcloud_talk, files, distill, auth, orchestrator
-from routers import ui, onboarding, settings, help, auth_google, local_llm
+from routers import ui, onboarding, settings, help, auth_google, local_llm, push
 
 
 @asynccontextmanager
@@ -34,6 +34,7 @@ app.include_router(files.router)
 app.include_router(distill.router)
 app.include_router(auth.router)
 app.include_router(orchestrator.router)
+app.include_router(push.router)
 
 # Static files — must be mounted BEFORE ui.router so /static/* is matched first.
 # ui.router has a wildcard /{username}/{persona} that would otherwise catch /static/style.css etc.