fix(desktop): keep rollback apps out of Applications

[0xSero]

Tasks

• store stable and dev rollback copies as validated ZIP archives outside /Applications
• migrate and unregister legacy Local Studio bundles without reinstalling the app
• stage replacements transactionally and restore the current app when verification fails
• audit tracked operational scripts for discoverable app-backup patterns
• document the migration workflow

Validation

• npm run check
• bash -n scripts/install-desktop-app.sh
• shellcheck scripts/install-desktop-app.sh
• live migration left exactly Local Studio.app and Local Studio Dev.app in /Applications
• both migrated rollback archives pass unzip integrity checks
• stale LaunchServices rollback registrations removed