ci: add build step to CI workflow

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

Author: DhruvBhatia0

.github/workflows/ci.yml

@@ -26,3 +26,6 @@ jobs:
 
       - name: Typecheck
         run: bun run typecheck
+
+      - name: Build
+        run: bun run build