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/repository.py

@@ -237,6 +237,29 @@ async def get_unread_count_for_chat(db: AsyncSession, *, chat_id: int, user_id:
     return int(result.scalar_one() or 0)
 
 
+async def get_last_visible_message_for_user(
+    db: AsyncSession,
+    *,
+    chat_id: int,
+    user_id: int,
+) -> Message | None:
+    stmt = (
+        select(Message)
+        .outerjoin(
+            MessageHidden,
+            (MessageHidden.message_id == Message.id) & (MessageHidden.user_id == user_id),
+        )
+        .where(
+            Message.chat_id == chat_id,
+            MessageHidden.id.is_(None),
+        )
+        .order_by(Message.id.desc())
+        .limit(1)
+    )
+    result = await db.execute(stmt)
+    return result.scalar_one_or_none()
+
+
 async def get_chat_notification_setting(
     db: AsyncSession, *, chat_id: int, user_id: int
 ) -> ChatNotificationSetting | None: