ci(embedded-e2e): build SDK and configure test environment

- Add a build-embedded-sdk step to bashlib.sh and wire it into the
  superset-playwright and superset-e2e workflows so the SDK bundle is
  compiled before Playwright runs.
- Set SUPERSET_FEATURE_EMBEDDED_SUPERSET=true via workflow env so the
  feature flag only affects Playwright jobs. Setting it in the shared
  integration test config breaks unrelated Python tests because the
  security manager's guest-user paths access g.user through paths that
  most tests don't mock.
- Add CORS for localhost:9000 and TALISMAN_ENABLED=False to the
  integration test config. Talisman defaults to X-Frame-Options:
  SAMEORIGIN, which blocks the embedded dashboard from rendering
  inside an iframe hosted on a different port.

.github/workflows/superset-e2e.yml

@@ -169,6 +169,7 @@ jobs:
       PYTHONPATH: ${{ github.workspace }}
       REDIS_PORT: 16379
       GITHUB_TOKEN: ${{ github.token }}
+      SUPERSET_FEATURE_EMBEDDED_SUPERSET: "true"
     services:
       postgres:
         image: postgres:17-alpine
@@ -239,6 +240,11 @@ jobs:
         uses: ./.github/actions/cached-dependencies
         with:
           run: build-instrumented-assets
+      - name: Build embedded SDK
+        if: steps.check.outputs.python || steps.check.outputs.frontend
+        uses: ./.github/actions/cached-dependencies
+        with:
+          run: build-embedded-sdk
       - name: Install Playwright
         if: steps.check.outputs.python || steps.check.outputs.frontend
         uses: ./.github/actions/cached-dependencies