feat(quality): Fase 4b — coverage ratchet (conservative floors, CI consumes merged coverage)

- quality-baseline.json: coverage.{statements,lines,functions,branches} floors (80/80/82/73, real ~82.58/82.58/84.23/75.22 with margin; tighten via --update after a green main run)
- check-quality-ratchet.mjs: --allow-missing (local quality:gate skips coverage.* without a coverage run; CI runs strict)
- ci.yml quality-gate job: needs test-coverage + downloads merged coverage-report so the ratchet enforces 'coverage cannot drop'
- TDD +1 test (6 total)

.github/workflows/ci.yml

@@ -52,6 +52,8 @@ jobs:
   quality-gate:
     name: Quality Ratchet
     runs-on: ubuntu-latest
+    needs: test-coverage
+    if: ${{ always() && needs.test-coverage.result == 'success' }}
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
@@ -59,6 +61,11 @@ jobs:
           node-version: ${{ env.CI_NODE_VERSION }}
           cache: npm
       - run: npm ci
+      # Coverage mergeada (coverage-summary.json) p/ o ratchet de cobertura.
+      - uses: actions/download-artifact@v8
+        with:
+          name: coverage-report
+          path: coverage/
       - run: npm run quality:collect
       # Catraca: falha se qualquer métrica regredir vs quality-baseline.json (commitado).
       # Hoje: contagem de warnings do ESLint. Fase 4 estende com cobertura (lida do