fix: use python3 for correctness checks and add CI (#50)

The benchmark harness hardcoded `python`, which is missing on macOS and
many Linux images. Probe python3 first, add npm test, and run checks in
GitHub Actions so regressions are caught on every PR.

Co-authored-by: Cursor <cursoragent@cursor.com>

.github/workflows/test.yml

@@ -0,0 +1,29 @@
+name: test
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Install Python deps for correctness checks
+        run: pip install pandas
+
+      - name: Check rule copies
+        run: node scripts/check-rule-copies.js
+
+      - name: Run tests
+        run: npm test