Remove the `issues: labeled` trigger from the timer workflow.
When both workflows triggered on label addition, the comment workflow
would post the bot comment, and by the time the timer workflow ran,
issue-manager would see "a comment was added after the label" and
immediately remove the label due to `remove_label_on_comment: true`.
The timer workflow now only runs on:
- Daily cron (to close stale issues)
- issue_comment (to remove label when humans respond)
- workflow_dispatch (for manual testing)