feat: add scheduler jobs, config persistence, and jobs API/CLI

[BadgerOps]

Summary

• add serve-mode scheduler (15s poll) to execute recurring sync/validate jobs from SQLite
• add shared job service for cron validation/next-run computation and job execution
• add jobs management surfaces across CLI (jobs list/add/pause/resume/run-now/delete), API (/api/jobs routes), and UI (/jobs)
• implement persistent config set KEY VALUE with typed YAML parsing and fallback ./airgap.yaml creation
• update store job APIs/migration and refresh docs/changelog for new behavior

Testing

• go test ./...
• python3 scripts/validate_versions.py