GalleryService.UpdateNodeProgress(opID, nodeID, np) merges a NodeProgress
into OpStatus.Nodes (keyed by NodeID, no duplicates) and mirrors the
latest tick into the aggregate Progress / FileName /
DownloadedFileSize / TotalFileSize fields so the legacy single-bar
OperationsBar view keeps working unchanged alongside the new per-node
breakdown.
Concurrent-safe via the existing g.Mutex.
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>