moderation: add chat bans for groups/channels with web actions

docs/api-reference.md

@@ -747,6 +747,17 @@ Response: `200` + `ChatMemberRead`
 Auth required.  
 Response: `204`
 
+### POST `/api/v1/chats/{chat_id}/bans/{user_id}`
+
+Auth required (`owner/admin` in group/channel).  
+Response: `204`  
+Behavior: bans user from chat and removes membership if present.
+
+### DELETE `/api/v1/chats/{chat_id}/bans/{user_id}`
+
+Auth required (`owner/admin` in group/channel).  
+Response: `204`
+
 ### POST `/api/v1/chats/{chat_id}/leave`
 
 Auth required.  

docs/core-checklist-status.md

@@ -31,7 +31,7 @@ Legend:
 22. Text Formatting - `PARTIAL` (bold/italic/underline/spoiler/mono/links + strikethrough + quote/code block; toolbar still evolving)
 23. Groups - `PARTIAL` (create/add/remove/invite link; advanced moderation partial)
 24. Roles - `DONE` (owner/admin/member)
-25. Admin Rights - `PARTIAL` (delete/ban-like remove/pin/edit info; full ban system limited)
+25. Admin Rights - `PARTIAL` (delete/pin/edit info + explicit ban API for groups/channels; remaining UX moderation tools limited)
 26. Channels - `PARTIAL` (create/post/edit/delete/subscribe/unsubscribe; UX edge-cases still polishing)
 27. Channel Types - `DONE` (public/private)
 28. Notifications - `PARTIAL` (browser notifications + mute/settings; no mobile push infra)