📌(frontend) pin yjs globally

We had a warning about yjs multiple versions
between dependencies. We pinned yjs globally
to avoid this warning and potential side effects.

src/frontend/package.json

@@ -40,6 +40,7 @@
     "eslint": "8.57.0",
     "react": "18.3.1",
     "react-dom": "18.3.1",
-    "typescript": "5.8.2"
+    "typescript": "5.8.2",
+    "yjs": "13.6.23"
   }
 }