ci: add missing highlight build step to app-tests job

The app-tests CI job was missing the `npm run build --workspace=@getpaseo/highlight`
step that all other jobs have. This caused diff-highlighter.test.ts to fail with
"Failed to resolve entry for package @getpaseo/highlight" because the dist/ directory
did not exist.

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

.github/workflows/ci.yml

@@ -88,6 +88,9 @@ jobs:
       - name: Install dependencies
         run: npm install
 
+      - name: Build highlight dependency
+        run: npm run build --workspace=@getpaseo/highlight
+
       - name: Run app unit tests
         run: npm run test --workspace=@getpaseo/app