upgrade: adopt V8.31.1 (theme 1.3/1.4 redesigns, editor deep-canvas, guided launch, component library)

Overlay 190 upstream items (V8.22→8.31) preserving trade-pro theme,
registry tests, and design docs. Re-applied full patch set on identical
anchors (discovery/env_for/blocks.css/type-mapping/locale-override/
theme_color/frontend entries/test_theme_pro_v3 mods) plus compose pins.

Verified: theme suites 35/35; dual-baseline full run 415 passed vs
pristine 386+29 ours, FAILED-set diff EMPTY (same 10 Windows env fails).
Live: container 8.31.1-dev.1 healthy, hesupipe 192 entries intact,
trade-pro build 203 pages 0 errors.

Co-Authored-By: Claude Code <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -28,14 +28,14 @@ jobs:
           SITEFORGE_SESSION_SECRET: ci-only-session-key-not-for-production-with-entropy
           SITEFORGE_PG_PASSWORD: ci-only-test-postgresql-password
         run: |
-          SITEFORGE_REGRESSION_REPEAT=2 bash scripts/check.sh
+          bash scripts/check.sh
           python scripts/http_end_to_end.py
-      - name: Upload V8.21 regression evidence
+      - name: Upload V8.23 regression evidence
         if: always()
         uses: actions/upload-artifact@v4
         with:
-          name: v821-regression-${{ matrix.python }}
-          path: reports/v821-regression*
+          name: v823-regression-${{ matrix.python }}
+          path: reports/v823-regression*
           if-no-files-found: ignore
           retention-days: 14
   browser-smoke:
@@ -58,6 +58,7 @@ jobs:
         run: |
           mkdir -p reports/browser
           python scripts/browser_smoke.py reports/browser
+          python scripts/studio_nested_browser_v823.py
       - name: Upload browser screenshots
         if: always()
         uses: actions/upload-artifact@v4