Feature request: add flag to disable activation/fallback comments

[strawgate]

Problem

After recent upgrades, workflows that create PRs can post extra bot comments like:

• ✅ Pull request created: #...

This happens via activation-comment update/fallback logic when GH_AW_COMMENT_ID is missing. These comments are outside the expected safe-output payload flow and add noise in repos that want silent automation.

Current behavior

• messages.append-only-comments controls edit-vs-new-comment behavior for status updates.
• There is no documented/frontmatter setting to disable activation comments entirely (including fallback creation comments).

Request

Please add a frontmatter/safe-outputs option to disable activation/fallback comments, e.g.:

safe-outputs:
  messages:
    activation-comments: false

(or equivalent naming)

Why

Some repos want safe-output actions (create PR/issue/etc.) without additional informational bot comments unless explicitly requested.

[pelikhan]

@copilot move the activation comments under safe-outputs:

safe-outputs:
  activation comments: false