- Add interruptible stop events to background workers so shutdown
wakes out of long sleeps instead of waiting on fixed delays.
- Stop scan managers, repair worker, executors, and cleanup helpers
deterministically so process exit does not leave background threads
alive.
- Add startup warnings for stale SQLite WAL/SHM sidecars so unclean
shutdowns are easier to spot before init/migration errors cascade.
- Prevent forced kills from leaving SQLite sidecars behind, which
made rollbacks to older branches fail with malformed database
errors.
