Add optional KEEP_LOCAL_BACKUP environment variable to control local backup retention.
Default behavior remains unchanged: backup files are deleted locally after
successful upload, keeping deployments safe on Railway and other PaaS
platforms with ephemeral storage.
When KEEP_LOCAL_BACKUP=true is set, backups are preserved locally, which is
useful for CLI usage, local machines, VPS, or NAS workflows.
Documentation and CLI output were updated for clarity.
No breaking changes.
KakiFilem Team