Add screenshot cleanup and NAS quarantine features

- NASTransferProtocol: add deleteFile(at:) to enable server-side deletion
- SFTPService: implement deleteFile using Citadel sftp.remove(at:)
- SMBService: implement deleteFile using SMBClient deleteFile(path:)
- SyncView FREE UP SPACE: two new cards —
  • "Clean up screenshots" — shows count of phone screenshots already
    backed up to NAS, opens review sheet for bulk PHPhotoLibrary deletion
  • "NAS screenshot quarantine" — identifies NAS files that match phone
    screenshots, offers to move them into a Screenshots/ subfolder via
    download → writeData → deleteFile per file

Co-Authored-By: Kutesir <kutesir@provoc.ug>
Co-Authored-By: Sentry <sentry@provoc.ug>

Core/Protocols/NASTransferProtocol.swift

@@ -25,4 +25,5 @@ protocol NASTransferProtocol: AnyObject {
     ) async throws
     func downloadData(at remotePath: String) async throws -> Data
     func writeData(_ data: Data, to remotePath: String) async throws
+    func deleteFile(at remotePath: String) async throws
 }