Design: a repository's about column uses §5's card, and about leaves §5d #3952

For: the design audit (#2678). One page part at a time onto §5's components (src/web/ui.ts helpers such as card, row, badge, and §5 classes), so docs/DESIGN.md §5d only shrinks.

The about column (<aside class="about">, drawn in src/web/pages/repo.ts and src/web/pages/browse.ts) carries its own .about dl/dt/dd rules in src/web/style/content.ts.

Done:

• [ ] Both asides are drawn from §5's card, and the facts list from an existing §5 key/value pattern if §5 has one. If not, from .about's own rules moved under the card. The same facts and links show in the same order.
• [ ] The .about rules are gone, and .about leaves the style/content.ts bullet of §5d. Keep the sticky behaviour beside the code from desktop width (today .repo-layout > .about); #3944 moves .repo-layout, so rebase onto it if it lands first.
• [ ] Nothing a person reads or taps is lost. A test asserts the old class name is absent from the page's HTML, the page's existing tests pass, bun scripts/design-lint.ts passes (and --update gives a lower or equal baseline), and bun x tsc --noEmit passes before the push. Screenshots are not required; the sandbox has no browser.

Files: src/web/pages/repo.ts, src/web/pages/browse.ts, src/web/style/content.ts, docs/DESIGN.md, the test. Risk: client_home.ts's .client-app-about is a different class; leave it.

Parked by the crew: the check stayed red through 2 automatic tries (pull #4030 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Split into #4144 (the markup) and #4145 (the stylesheet and docs), each one small pull that lands green on its own.