docs/design/audit.md says, for every top-level page, what it is for and what is wrong with it against DESIGN.md #2709

For #2678. Written from source, no screenshots needed (those come from the look of every page).

Done:

• [ ] docs/design/audit.md has one entry per top-level page: route, the module that renders it, what it is for in one sentence, what duplicates it, and what breaks docs/DESIGN.md (colours or sizes outside the tokens in section 2, components outside section 5)
• [ ] a closing section names the pages to merge or retire (matching #2692–#2696) and what the clean app template (src/apps/scaffold.ts) does better
• [ ] test: every top-level route has an entry, and the doc names no route that does not exist

Files: docs/design/audit.md, one test. Risk: none at runtime.