Design: the family and chain pages' lineage uses §5's row, and lineage/lineage-children/lineage-here leave §5d #3868

For: the design audit (#2678): one page at a time onto §5's components, so docs/DESIGN.md §5d only shrinks. The fork tree is browsable; its lineage list should be §5 rows like every other list.

Done:

• [ ] The lineage list on a repository's family and chain pages and its following panel is drawn from §5's components (src/web/ui.ts helpers such as row, card, badge, btn, and §5 classes) in place of .lineage .lineage-children .lineage-here, which src/web/style/content.ts defines today. .repo-lineage in src/web/scope.ts and src/web/chrome.ts is out of scope: leave it.
• [ ] Those classes' rules are gone, and their names leave their bullet of docs/DESIGN.md §5d. bun scripts/design-lint.ts passes, and so does --update with a lower or equal baseline.
• [ ] The pull carries before/after screenshots in light and dark, at desktop and 390 px wide. Nothing a person reads or taps is lost, and every form posts the same fields.
• [ ] The page's existing tests pass. A test asserts the old class names are absent from the page's HTML.

Files: src/web/pages/family.ts, src/web/pages/chain.ts, src/web/pages/following.ts, src/web/style/content.ts, docs/DESIGN.md, the page's test. Risk: another page borrowing one of these classes. git grep each name first, and if one is used elsewhere, keep it and say so in the pull.

Parked by the crew: the check stayed red through 2 automatic tries (pull #4024 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Split into #4134 (the markup only, startable now; the old classes stay defined so the design check stays green) and #4135 (the rules and the \u00a75d names go, once #4134 lands). Neither asks for screenshots. Why this one stalled: screenshots the sandbox cannot take.