Design: the where-am-I trail uses the design system, and where-dot/where-note/where-sep leave §5d #3875

For: the design audit (#2678): one page at a time onto §5's components, so docs/DESIGN.md §5d only shrinks. Never lost: the trail that says where a page sits should be one §5 component on every page.

Done:

• [ ] The where-am-I trail built in src/web/scope.ts (and the search, origins and site pages that draw it) is drawn from §5's components (src/web/ui.ts helpers such as row, card, badge, btn, and §5 classes) in place of .where-dot .where-note .where-sep, which src/web/style/content.ts defines today. src/tui/app/palette.ts names where-dot for the terminal: leave the terminal as it is.
• [ ] 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/scope.ts, src/web/pages/search.ts, src/web/pages/origins.ts, src/web/pages/site.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.