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/channels/groups.md

@@ -43,6 +43,10 @@ otherwise -> reply
 For group/channel rooms, OpenClaw defaults to `messages.groupChat.visibleReplies: "message_tool"`.
 That means the agent still processes the turn and can update memory/session state, but its normal final answer is not automatically posted back into the room. To speak visibly, the agent uses `message(action=send)`.
 
+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.
+
 For direct chats and any other source turn, use `messages.visibleReplies: "message_tool"` to apply the same tool-only visible-reply behavior globally. `messages.groupChat.visibleReplies` remains the more specific override for group/channel rooms.
 
 This replaces the old pattern of forcing the model to answer `NO_REPLY` for most lurk-mode turns. In tool-only mode, doing nothing visible simply means not calling the message tool.