v3.0.24: feat(backup): implement automatic scheduled backups and recovery

- Add configuration fields for scheduled backups to AppConfig in
  src/config.rs, including enabled status, interval, and retention count.
- Introduce a background backup scheduler in src/cmd/serve.rs that runs
  periodically based on the defined interval.
- Implement backup rotation in src/data/backup_manager.rs to maintain a
  fixed number of recent backups.
- Add robust automatic recovery in src/data/repository.rs: if the database
  fails to open, the application now attempts to restore the latest
  verified-good backup from the backup folder, renaming the corrupt
  database file for forensic preservation.
- Introduce BackupFileLock in src/ipc.rs, a low-level file lock that
  allows long-running background tasks (like the scheduler) to safely
  manage backup mutual exclusion without triggering premature process
  exits, separating this logic from the CLI-specific OperationLock.
- Consolidate backup filename generation and listing logic in
  src/data/backup_manager.rs to standardize backup handling across both
  manual CLI commands and the new automated system.
- Add unit and integration tests for backup rotation, name generation,
  and recovery behavior to ensure system reliability during data
  corruption events.