fix: install libGL/libEGL runtime deps, set offscreen platform for tests

PySide6 imports fail with 'libGL.so.1: cannot open shared object file' on
the headless self-hosted runner. Install the libraries and set
QT_QPA_PLATFORM=offscreen to avoid needing a display for unit tests.

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

Author: chrisdpurcell

.github/workflows/ci.yml

@@ -27,7 +27,14 @@ jobs:
     - name: Install dependencies
       run: uv pip install --system -r requirements.txt
 
+    - name: Install Qt runtime dependencies
+      run: |
+        sudo apt-get update -q
+        sudo apt-get install -y libgl1 libegl1 libxkbcommon-x11-0
+
     - name: Run tests
+      env:
+        QT_QPA_PLATFORM: offscreen
       run: pytest tests/ -v --cov=src --cov-report=xml --cov-fail-under=80
 
     - name: Upload coverage to Codecov