ci(ubicloud): run kicad e2e under xvfb — headed firefox for software WebGL

Same rationale as the Hetzner workflow change in 3168eff: headless Firefox
cannot create any GL context on the GPU-less runner.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/ci-ubicloud.yml

@@ -36,7 +36,10 @@ jobs:
         run: |
           export DEBIAN_FRONTEND=noninteractive
           sudo apt-get update
-          sudo apt-get install -y cmake ninja-build g++ libjemalloc2
+          # xvfb: kicad e2e runs headed Firefox under a virtual display — headless
+          # Firefox cannot create any GL context on the GPU-less VM (see
+          # tests/playwright-kicad.config.ts CI prefs).
+          sudo apt-get install -y cmake ninja-build g++ libjemalloc2 xvfb
 
       - uses: actions/checkout@v4
         with: { submodules: recursive }
@@ -81,7 +84,9 @@ jobs:
 
       - name: KiCad e2e (npm run test:kicad)
         working-directory: tests
-        run: npm run test:kicad
+        # xvfb-run: headed Firefox on a virtual display — WebGL needs GLX + Mesa
+        # llvmpipe, which headless Firefox can't reach on a GPU-less VM.
+        run: xvfb-run -a npm run test:kicad
 
       - name: Upload test logs & screenshots
         if: always()