docs: promote the working notes — design doc, audit findings, brand export, task logs

[matthewpmunger]

What

Promotes the untracked working files that accumulated at the repo root:

• DESIGN.md — the design doc for whoever picks up a chunk next. Known staleness, promoted as-is: it cites vocabulary.json v9 (13 concepts, 21 rules) while the registry is at v10. By the doc's own rule ("where the two disagree, the registry wins and this file is the bug") this is a bug in the doc; left for the author to reconcile rather than edited in a promotion PR.
• AUDIT-FINDINGS.md — independent review of AUDIT-RECONCILIATION.md, pinned to 95d77a9. Its headline finding (S5 merged on neither tip) has since been resolved by S5 — an owner and a start date on the case, and the task board retired #84. A dated review artifact stays accurate about the sha it names.
• brand/ — brand-system export (brand-systems.json + the system's own copy of DESIGN.md, which differs from the root copy; that divergence is inherent to the export format).
• .webflow/tasks/*.log (9 files) — fourteen sibling logs are already tracked, so these follow precedent. Several are 34-byte npm: command not found stubs; if the preference is to gitignore .webflow/tasks/ instead, happy to swap this commit for that.

Two commits: docs in one, logs in the other, so either can be dropped alone.

Base

Base: f52362c (main, green — merged via #84 with all checks passing).
Checks at 5099ba9: npm run lint ✓ · npm run typecheck ✓ · npm test -- --run ✓ (107 files, 1393 tests). No code changes; no dependency/lockfile changes.