Use host IP for e2e test API in CI

The act runner executes steps inside a container where localhost does
not reach the Docker host. Use E2E_API_URL env var (set to the host IP
192.168.1.10:8100 in CI) so both the global setup and Vite proxy can
reach the test API container.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -91,6 +91,8 @@ jobs:
       - name: Run e2e tests
         run: npm run test:e2e
         working-directory: frontend
+        env:
+          E2E_API_URL: http://192.168.1.10:8100
       - name: Upload Playwright report
         if: failure()
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02  # v4.6.2