docs: design lab is tracked twice — docs/design-lab (stale) and branding/design-lab (canonical)

[Xore]

main carries two copies of the design lab:

• branding/design-lab/ — 12 files, added by docs(branding): preserve the design lab before the job holding it is deleted #1827 (f9575d6), extended by feat(design-lab): serve variants against real data, without being able to write #1935 (lab.mjs, lab.test.mjs). This is the canonical location (branding/ is the visual spec).
• docs/design-lab/ — 10 files, added incidentally by fix(dashboard): a11y basics — skip link, toast live region, combobox palette, keyboard-reachable workbench cards; restore canonical link tokens (design audit P3) #3182 (526eaf5, an a11y PR) on 2026-09-14. Content is the original The design lab that produced the current design exists only in a deletable job temp dir — preserve it before the multi-theme work #1763 snapshot (f661452): 9 files byte-identical to that commit, playground/compare.html slightly newer.

Against branding/design-lab/, the docs/ copy has older README.md, design-notes.md, playground/compare.html and playground/elements.html, and lacks lab.mjs/lab.test.mjs. Anyone editing the docs/ copy edits a dead fork.

Proposal

Before deleting: grep the repo (docs links, CI, Pages workflow, compose mounts) for docs/design-lab references and repoint them to branding/design-lab; diff playground/compare.html between the two copies and fold any change only the docs/ copy has into branding/. Then remove docs/design-lab/.

[Xore]

Implemented and merged in PR #3437.