fix(channel): member delete acts as leave; add coverage and docs

docs/api-reference.md

@@ -802,6 +802,14 @@ Response: `204`
 Auth required.  
 Response: `204`
 
+Behavior:
+
+- `saved messages`: clears personal history only (chat is not removed).
+- `channel` + role `owner/admin`: deletes channel for all members.
+- `channel` + role `member`: acts as leave channel (removes only current membership).
+- `group/private` with `for_all=false`: removes chat for current user only.
+- `for_all=true` (where allowed): deletes chat globally.
+
 ### POST `/api/v1/chats/{chat_id}/clear`
 
 Clear chat history for current user.

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/pin/edit info + explicit ban API for groups/channels; remaining UX moderation tools limited)
+25. Admin Rights - `PARTIAL` (delete/pin/edit info + explicit ban API for groups/channels; channel member delete now behaves as leave, 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)