feat: mentions badge in chat list and muted-mention delivery

docs/api-reference.md

@@ -190,6 +190,7 @@ All fields are optional.
   "archived": false,
   "pinned": false,
   "unread_count": 3,
+  "unread_mentions_count": 1,
   "pinned_message_id": null,
   "members_count": 2,
   "online_count": 1,
@@ -748,6 +749,8 @@ Body:
 
 Response: `200` + `ChatNotificationSettingsRead`
 
+Note: mentions (`@username`) are delivered even when chat is muted.
+
 ### POST `/api/v1/chats/{chat_id}/archive`
 
 Auth required.  
@@ -935,4 +938,3 @@ Configured via env vars:
 - Invite links are generated for group/channel chats.
 - In channels, only users with sufficient role (owner/admin) can post.
 - `email` router exists in codebase but has no public REST endpoints yet.
-