* perf(app): defer inactive Code panel generation
- Skip JSX serialization and syntax highlighting while the Code tab is hidden
- Restore code generation when desktop or mobile users activate the tab
- Cover large Design-tab selections without hidden Code-panel work
* test(app): cover deferred Code panel updates
- Keep mobile JSX generation inactive while the drawer is closed
- Measure the complete two-frame inactive selection flow
- Verify mobile Code output refreshes when the drawer reopens
