fix: increase Node heap size for frontend build in CI

Exit code 134 (OOM) during vite build on GitHub Actions runner.
Add NODE_OPTIONS=--max-old-space-size=4096 to the build step.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -93,7 +93,7 @@ jobs:
         run: cd frontend && npm run test:coverage
 
       - name: Build
-        run: cd frontend && npm run build
+        run: cd frontend && NODE_OPTIONS="--max-old-space-size=4096" npm run build
 
   e2e:
     runs-on: ubuntu-latest