Add async migration operation mode

[KeKs0r]

Summary

• add opt-in mode=async migration operations with deterministic query ids and resumable polling
• persist per-operation journal state for started/completed/failed async work
• support before-retry compensation before resubmitting interrupted async operations
• guard retries when in-progress journal state was written for a different migration checksum
• update ClickBench to load from the ObsessionDB-hosted mirror using async mode

Verification

• bun test packages/cli/src/test/commands/migrate/async-apply.test.ts packages/cli/src/test/runtime/journal-store.test.ts packages/cli/src/test/runtime/safety-markers.test.ts