SEV-1 backfill — re-scrub stored articles whose body_text matched the leak detector, enqueue fresh render jobs, surface affected publishers for outreach. See app.pii_backfill for the matcher + scrub semantics.

Body params:

• dry_run (default True): report counts without writing
• limit (default 1000, max 5000): cap rows scanned per call
• also_delete_old_audio (default False): currently logged as TODO; re-render writes the new audio to the same R2 key so listeners get the clean version on next play anyway.