The front page's hero and terminal line draw §5's card and row, and .hero, .hero-terminal leave the markup #4170

Part one of #3870, which went red as one change. This part changes only the markup; the stylesheet and docs/DESIGN.md are part two.

Done:

• [ ] The front page's hero and its terminal line are drawn with §5's card and row from src/web/ui.ts and §5's classes. None of .hero .hero-terminal appears in the page's HTML. The terminal line still prints FORGE_APP_SSH verbatim when it is set, and says the terminal is off when it is not.
• [ ] Do not delete the rules from src/web/style/content.ts and do not edit docs/DESIGN.md. Part two does that, and the design check stays green because the classes are still defined and named.
• [ ] Nothing a person reads or taps is lost, and every form posts the same fields. A test asserts the old names are absent and the words, links and forms are present.

Files: src/web/studio/home.ts, a test. Before pushing, run bun x tsc --noEmit, bun test test/design-lint.test.ts and the page's tests. No screenshots: the sandbox has no browser.