ci: add GitHub Actions workflow to run tests on PRs (#307)

Runs pytest suite across Python 3.11, 3.12, and 3.13 on ubuntu-latest.
Agent-dependent tests auto-skip via existing conftest logic.
Triggers on PRs targeting master and pushes to master.

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

.github/workflows/tests.yml

@@ -0,0 +1,30 @@
+name: Tests
+
+on:
+  pull_request:
+    branches: [master]
+  push:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ['3.11', '3.12', '3.13']
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install pyyaml>=6.0 pytest pytest-timeout
+
+      - name: Run tests
+        run: pytest tests/ -v --timeout=60