feat: file manager with browse, search, upload, chmod/chown
- Full file browser page at /files with lazy-load, breadcrumbs, drag&drop
- FileBrowserModal component for path selection from Samba/NFS forms
- PathField component replaces bare inputs in share/export forms
- Backend: /api/files/* routes with List, Mkdir, Rename, Delete, Chmod, Chown, Upload, Download, Preview, Search
- Reuses NASCTL_ALLOWED_ROOTS for path validation
- NASCTL_UPLOAD_MAX_BYTES (100MB) and NASCTL_PREVIEW_MAX_BYTES (256KB) env vars
- Capabilities endpoint returns chmod/chown availability (requires root)
- Version bump: 0.3.2 -> 0.4.0
darroyo
50ed8abe95