Add build and dist/ freshness check to CI

The CI workflow only ran tests without rebuilding dist/, so dependency
updates (e.g. from Dependabot) would be merged with stale compiled JS
built from the previous toolchain. Now CI rebuilds and fails if dist/
is out of date.

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

.github/workflows/unit-tests.yml

@@ -21,5 +21,16 @@ jobs:
       - name: Install dependencies
         run: npm ci
 
+      - name: Build
+        run: npm run build
+
+      - name: Check dist/ is up-to-date
+        run: |
+          if [ -n "$(git diff --name-only)" ]; then
+            echo "::error::dist/ is out of date. Run 'npm run build' and commit the changes."
+            git diff --name-only
+            exit 1
+          fi
+
       - name: Run tests
         run: npm test