feat: realtime sync, settings UX and chat list improvements

- add chat_updated realtime event and dynamic chat subscriptions

- auto-join invite links in web app

- implement Telegram-like settings panel (general/notifications/privacy)

- add browser notification preferences and keyboard send mode

- improve chat list with last message preview/time and online badge

- rework chat members UI with context actions and role crowns

app/realtime/schemas.py

@@ -17,6 +17,7 @@ RealtimeEventName = Literal[
     "message_delivered",
     "user_online",
     "user_offline",
+    "chat_updated",
     "pong",
     "error",
 ]