- Cleans expired verifications and orphaned usage rows
- Previously only ran once on startup (13d+ uptime = accumulation)
- Interval uses .unref() to not block graceful shutdown
- Stopped during shutdown before pool.end()
- Idempotent start (safe to call multiple times)
- 6 TDD tests added (periodic-cleanup.test.ts)
- 663 tests total, all passing
