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>

Services/SMBService.swift

@@ -119,6 +119,13 @@ final class SMBService: NASTransferProtocol {
         }
     }
 
+    func deleteFile(at remotePath: String) async throws {
+        guard let client else { throw BackupError.connectionFailed("Not connected") }
+        let (share, rel) = splitPath(remotePath)
+        try await client.connectShare(share)
+        try await client.deleteFile(path: rel)
+    }
+
     func upload(localURL: URL, remotePath: String, progress: @escaping (Int64, Int64) -> Void) async throws {
         guard let client else { throw BackupError.connectionFailed("Not connected") }
         let (share, rel) = splitPath(remotePath)