fix(auto-reply): move visible reply warnings to doctor (#75367)

Summary:
- The PR removes the auto-reply runtime warning for visible-reply defaults, adds doctor preview warnings and tests for message-tool visibility policy mismatches, and updates the group/channel docs and changelog wording.

ClawSweeper fixups:
- No separate fixup commits were needed after automerge opt-in.

Validation:
- ClawSweeper review passed for head 1f96b3b568.
- Required merge gates passed before the squash merge.

Prepared head SHA: 1f96b3b568
Review: https://github.com/openclaw/openclaw/pull/75367#issuecomment-4357475980

Co-authored-by: Peter Steinberger <steipete@gmail.com>

docs/gateway/config-channels.md

@@ -772,6 +772,8 @@ Group messages default to **require mention** (metadata mention or safe regex pa
 
 Visible replies are controlled separately. Group/channel rooms default to `messages.groupChat.visibleReplies: "message_tool"`: OpenClaw still processes the turn, but normal final replies stay private and visible room output requires `message(action=send)`. Set `"automatic"` only when you want the legacy behavior where normal replies are posted back to the room. To apply the same tool-only visible-reply behavior to direct chats too, set `messages.visibleReplies: "message_tool"`.
 
+If the message tool is unavailable under the active tool policy, OpenClaw falls back to automatic visible replies instead of silently suppressing the response. `openclaw doctor` warns about this mismatch.
+
 The gateway hot-reloads `messages` config after the file is saved. Restart only when file watching or config reload is disabled in the deployment.
 
 **Mention types:**