Updater v1 --upgrade + roadmap as flat backlog

Updater: watch-together --upgrade checks updates/manifest.json,
downloads the tarball, verifies sha256, applies over the live
install (extract-temp + delete-first move-over; rename-safe on
Linux while running). Zero Flutter imports, 7 tests incl.
stub-server flows. Version stamped via --dart-define=APP_VERSION
in package script. Warns (never silently jumps) on proto mismatch.
Roadmap: phases retired as tracker (history in git log), now flat
Built/Backlog/Epics/Deferred; Jellyfin next feature, transcode
never; updater expansion stays an epic. Endpoint publishing
(manifest + release tarball) is user-owned.

apps/desktop/lib/main.dart

@@ -8,8 +8,13 @@ import 'package:window_manager/window_manager.dart';
 
 import 'app.dart';
 import 'src/state/session_state.dart';
+import 'src/update/updater.dart';
 
 Future<void> main(List<String> args) async {
+  if (args.contains('--upgrade')) {
+    exitCode = await runUpgrade();
+    exit(exitCode);
+  }
   initLogging();
   if (args.contains('--headless')) {
     await runHeadless(args);