ci: add Python 3.12/3.13/3.14 matrix and coverage gate

- Add strategy.matrix for python-version: ["3.12", "3.13", "3.14"] on test job
- Add --cov-fail-under=80 to pytest invocation
- Lint job stays on single Python version (no matrix needed for style checks)

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

Author: chrisdpurcell

.github/workflows/ci.yml

@@ -9,14 +9,17 @@ on:
 jobs:
   test:
     runs-on: [self-hosted, linux, l3digital]
+    strategy:
+      matrix:
+        python-version: ["3.12", "3.13", "3.14"]
 
     steps:
     - uses: actions/checkout@v4
 
-    - name: Set up Python 3.14
+    - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v5
       with:
-        python-version: '3.14'
+        python-version: ${{ matrix.python-version }}
 
     - name: Install uv
       run: pip install uv
@@ -25,7 +28,7 @@ jobs:
       run: uv pip install --system -r requirements.txt
 
     - name: Run tests
-      run: pytest tests/ -v --cov=src --cov-report=xml
+      run: pytest tests/ -v --cov=src --cov-report=xml --cov-fail-under=80
 
     - name: Upload coverage to Codecov
       uses: codecov/codecov-action@v4