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/config.py

@@ -89,6 +89,12 @@ class Settings(BaseSettings):
     jwt_secret: str = "change-me-in-dotenv"   # override in .env: JWT_SECRET=<random>
     jwt_expire_days: int = 30
 
+    # Web Push (VAPID) — for browser push notifications
+    # Generate once with py_vapid; see push_utils.py for key format details
+    vapid_public_key: str = ""     # base64url-encoded uncompressed EC point (for browser)
+    vapid_private_key_b64: str = "" # base64-encoded PEM private key (single-line .env storage)
+    vapid_contact: str = "mailto:admin@example.com"
+
     # SMTP — for sending invite emails
     smtp_server: str = ""
     smtp_port: int = 465