New 'Updates' tab in the app detail page, beside Backups. Reuses the headless
UpdaterPage + renderAppDetail() scoped to the single app, so the per-app and
fleet views share one data/render path. UpdaterPage is added to the apps script
bundle so it's available on app pages; the tab is disabled while a task runs.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>