fix: NAS gallery shows backed-up files even when caches are cold

GalleryViewModel.load() now has a three-tier resolution for manifest entries:
  1. statusService.lastManifest — in-memory, freshest
  2. NASManifestCache disk cache — survives restarts
  3. Direct NAS download — fallback when both caches are cold (first launch after install,
     or before BackupStatusService reconcile has completed)

The direct download also populates NASManifestCache so subsequent opens are instant.

Also adds GalleryViewModel.bind(to:connection:) which subscribes to
statusService.$lastManifest and automatically reloads gallery items when
BackupStatusService finishes reconciling — gallery updates without manual pull-to-refresh.

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

Features/Browse/GalleryView.swift

@@ -36,6 +36,7 @@ struct GalleryView: View {
             )
         }
         .task {
+            viewModel.bind(to: statusService, connection: store.savedConnection)
             await viewModel.load(connection: store.savedConnection, statusService: statusService)
         }
         .refreshable {