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/chats/service.py

@@ -67,6 +67,7 @@ async def serialize_chat_for_user(db: AsyncSession, *, user_id: int, chat: Chat)
             subscribers_count = members_count
 
     unread_count = await repository.get_unread_count_for_chat(db, chat_id=chat.id, user_id=user_id)
+    last_message = await repository.get_last_visible_message_for_user(db, chat_id=chat.id, user_id=user_id)
     user_setting = await repository.get_chat_user_setting(db, chat_id=chat.id, user_id=user_id)
     archived = bool(user_setting and user_setting.archived)
     pinned = bool(user_setting and user_setting.pinned)
@@ -94,6 +95,9 @@ async def serialize_chat_for_user(db: AsyncSession, *, user_id: int, chat: Chat)
             "counterpart_username": counterpart_username,
             "counterpart_is_online": counterpart_is_online,
             "counterpart_last_seen_at": counterpart_last_seen_at,
+            "last_message_text": last_message.text if last_message else None,
+            "last_message_type": last_message.type if last_message else None,
+            "last_message_created_at": last_message.created_at if last_message else None,
             "my_role": my_role,
             "created_at": chat.created_at,
         }