- Add 'mfer export' command: dumps manifest as JSON to stdout for piping to jq etc
- Add HTTP/HTTPS URL support for manifest path arguments (check, list, export)
- Enable --version flag (was hidden, now shown)
- Audit all error messages: wrap with fmt.Errorf context throughout CLI and library
- Add tests for export command and URL-based manifest loading
- Add manifest_loader.go with shared resolveManifestArg and openManifestReader helpers
