fix: add yjs and y-prosemirror overrides to deduplicate Yjs

Prevents "Yjs was already imported" error by ensuring all packages
use the same Yjs instance.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: yoen-velt

package.json

@@ -47,7 +47,9 @@
       "@veltdev/blocknote-crdt-react": "4.5.0-beta.3",
       "@veltdev/codemirror-crdt-react": "4.5.8",
       "@veltdev/reactflow-crdt": "4.5.8",
-      "@veltdev/react": "^4.6.10"
+      "@veltdev/react": "^4.6.10",
+      "yjs": "^13.6.18",
+      "y-prosemirror": "^1.2.12"
     }
   }
 }