Safety net for messages marked closed by direct JSON edit instead of
drone @ai_mail close. _sweep_closed() in inbox_cleanup.py archives
closed messages to deleted/ and removes them from the inbox.
Wired into: mark_as_opened, mark_as_closed_and_archive (inbox_cleanup),
deliver_email_to_branch, deliver_to_inbox_file (delivery), and
load_inbox (inbox_ops). 8 new tests, 690 total pass.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
