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/service.py

@@ -144,6 +144,24 @@ class RealtimeGateway:
     async def load_user_chat_ids(self, db: AsyncSession, user_id: int) -> list[int]:
         return await list_user_chat_ids(db, user_id=user_id)
 
+    def add_chat_subscription(self, *, chat_id: int, user_id: int) -> None:
+        self._chat_subscribers[chat_id].add(user_id)
+
+    def remove_chat_subscription(self, *, chat_id: int, user_id: int) -> None:
+        subscribers = self._chat_subscribers.get(chat_id)
+        if not subscribers:
+            return
+        subscribers.discard(user_id)
+        if not subscribers:
+            self._chat_subscribers.pop(chat_id, None)
+
+    async def publish_chat_updated(self, *, chat_id: int) -> None:
+        await self._publish_chat_event(
+            chat_id,
+            event="chat_updated",
+            payload={"chat_id": chat_id},
+        )
+
     async def _handle_redis_event(self, channel: str, payload: dict) -> None:
         chat_id = self._extract_chat_id(channel)
         if chat_id is None: