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.

tool/package_linux.sh

@@ -30,7 +30,7 @@ VERSION="$(sed -n 's/^version: \([0-9.]*\).*/\1/p' "$APP/pubspec.yaml")"
 if [[ -z "$VERSION" ]]; then echo "error: version not found in $APP/pubspec.yaml" >&2; exit 1; fi
 
 if [[ "$SKIP_BUILD" != "1" ]]; then
-  (cd "$APP" && flutter build linux --release)
+  (cd "$APP" && flutter build linux --release --dart-define=APP_VERSION="$VERSION")
 fi
 
 BUNDLE="$APP/build/linux/$ARCH/release/bundle"