design-lint holds the quiet-page rules a machine can check, so new pages get them #8775

Follows #8719: the rules a machine can check should join scripts/design-lint.ts, so new pages (Next up, bets, Flow, Notes) get them without a review.

Done looks like:

• [x] design-lint refuses, with file:line and what to use instead: a "Status:" or similar label before a status word; small uppercase captions (text-transform: uppercase on a label class); an icon followed by its own label as the aria-label and visible text both; a colour literal outside the tokens.
• [x] What already breaks a rule on main is listed as debt in one place, naming the file, so the lint passes today and the list can only shrink.
• [x] A test feeds each rule a bad snippet and a good one.
• [x] docs/DESIGN.md is not edited. The rules are named in docs/design/areas/quiet.md.

Files: scripts/design-lint.ts, docs/design/areas/quiet.md (new), test/design-lint.test.ts Risks: false positives on prose. Match markup and style only, never the words in a paragraph.

Reviewed pull #8779 at its head: ticked design-lint refuses, with file:line and what to use instead: a "Status:" or similar label before a status word; small uppercase captions (text-transform: uppercase on a label class); an icon followed by its own label as the aria-label and visible text both; a colour literal outside the tokens.; What already breaks a rule on main is listed as debt in one place, naming the file, so the lint passes today and the list can only shrink.; A test feeds each rule a bad snippet and a good one.; docs/DESIGN.md is not edited. The rules are named in docs/design/areas/quiet.md..