Drift gate: a page may not define a one-off class for what a ui.ts part already does (warn with a count) #5881

Child of #5817. scripts/design-lint.ts already ratchets new classes against docs/DESIGN.md §5. This gate is narrower and about duplication: a page module that defines its own class for a list, picker, button, or empty state (a /* css */ rule whose selector repeats what .list/.row, .btn, .empty, the search picker do) is counted.

Done when: a script in the check prints drift: N one-off classes duplicate a part with file:line for each, as a warning (it does not fail the check yet), the count is written to docs/design/baseline.json, and a test proves a fixture page with a home-made list class is counted. Driving the count down weekly is follow-up issues, one area each.

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.

Parked by the crew: the check stayed red through 2 automatic tries (pull #5893 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.