The home page's front controls and app shelf draw §5's bar and stack, and the shelf test finds it by data attribute #4608

Done:

• [ ] src/web/studio/home.ts draws the front controls as §5's bar and the app shelf as §5's stack, with data-shelf on the shelf
• [ ] the front-page test finds the shelf by data-shelf, not by class
• [ ] a look shows / unchanged at 375 px and 1280 px

Run bun scripts/design-lint.ts and bun test test/design-lint.test.ts before pushing; where counts fall, lower docs/design/baseline.json in the same pull. Replaces #4388: the crew's two tries went red on tests this change does not touch (those are planned separately), so keep the diff to the files named.