ci: Add GitHub Actions workflow for automated testing

- Run tests on push and pull requests
- Test on Node.js 18, 20, and 22
- Run linter and build checks
- Upload coverage to Codecov
- Ensures code quality on every commit

🤖 Generated with Claude Code

Co-Authored-By: Claude <[email protected]>

Author: michaeloboyle

.github/workflows/ci.yml

@@ -0,0 +1,46 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [18.x, 20.x, 22.x]
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v4
+      with:
+        node-version: ${{ matrix.node-version }}
+        cache: 'npm'
+
+    - name: Install dependencies
+      run: npm ci
+
+    - name: Run linter
+      run: npm run lint --if-present
+
+    - name: Build
+      run: npm run build
+
+    - name: Run tests
+      run: npm test
+
+    - name: Check test coverage
+      run: npm run test:coverage
+
+    - name: Upload coverage to Codecov
+      if: matrix.node-version == '20.x'
+      uses: codecov/codecov-action@v3
+      with:
+        files: ./coverage/lcov.info
+        fail_ci_if_error: false