feat: add impeccable frontend skill + document quality test results

Add pbakaus/impeccable (v4.1.1, 23 design commands, 59 deterministic
anti-slop rules) to the frontend workflow and READMEs.

Document the QA harness measurements in both READMEs: before/after
workflow scores on the same ruler (total +98.6%), the four green gates,
the meta-tests, and what the refinement added. Full snapshot history
is in qa/snapshots/.

workflows/wf-frontend.md

@@ -31,7 +31,9 @@ Sempre que a tarefa envolver interface do usuário ou GERAÇÃO DE PDF:
 ## Skills do stack (carregar conforme a fase)
 
 - Direção visual / anti-AI-slop: `frontend-design` (Anthropic), `web-design`,
-  e locais `frontend-award-tier`, `claude-design`, `popular-web-designs`,
+  `impeccable` (pbakaus — 23 comandos de design: craft/shape/audit/polish/
+  animate/live; 59 regras determinísticas anti-slop), e locais
+  `frontend-award-tier`, `claude-design`, `popular-web-designs`,
   `anti-ai-slop`
 - React/Next performance + composição: `vercel-react-best-practices`,
   `vercel-composition-patterns`