feat(skill): absorb external design skills, restore interview gate, add review route

- Restore the step-0 interview as a mechanical gate the skill explicitly
  depends on; add harness.md (per-harness question tools, limits,
  fallbacks) and brief-interview.md (slots, question cards, rounds).
- Add 10 reference docs absorbed from external design skills
  (accessibility, interaction-feel, elevation, color, icons, product-copy,
  component-systems, critique, change-review, print-email) and extend
  existing references.
- Add a review-only route and two hard-gate clauses (truncated content
  reachability, three-flashes limit).
- design-gate: split tap targets into WCAG 2.5.8 and 44px contract layers,
  run axe-core when available, and fix false positives found on a real
  site (decorative alt="", stacked wordmark line count, url-only pages).
- lint-skill: fail if the interview gate section or its links disappear.
- Ship agents/openai.yaml and THIRD_PARTY_NOTICES.md.

packages/skill/agents/openai.yaml

@@ -0,0 +1,6 @@
+interface:
+  display_name: "designpaca"
+  short_description: "브리프 인터뷰부터 셀프 감사까지 이어지는 웹 디자인 파이프라인"
+
+policy:
+  allow_implicit_invocation: true