Add NFS/CIFS network mount management from UI

[nitrobass24]

Summary

Allow users to configure, mount, unmount, and test NFS/CIFS network shares directly from the Settings page.

Details

Users who download to a NAS currently need to configure Docker volume mounts manually. UI-managed network mounts simplify this workflow.

Implementation

• New network_mounts.json config file
• CRUD REST endpoints for mount definitions
• Mount/unmount/test actions from UI
• Mount types: NFS, CIFS/SMB
• Per-mount fields: name, type, server, share_path, username, password, domain, mount_options, enabled
• Mount option whitelist for security
• Password encrypted before storage, redacted from API responses
• Docker image needs nfs-common and cifs-utils packages

Acceptance Criteria

• NFS and CIFS mounts configurable from Settings
• Mount/unmount/test actions work from UI
• Credentials securely stored and redacted from API
• Mount options validated against whitelist