feat: added drag and drop menu for adding new nodes to flow

added a sidebar that supports drag and dropping new nodes from the sidebar into the flow editor.
also added a new package (neodrag) for easy draggable behavior outside the reactFlow editor.

ref: N25B-114

package.json

@@ -10,6 +10,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@neodrag/react": "^2.3.1",
     "@xyflow/react": "^12.8.6",
     "react": "^19.1.1",
     "react-dom": "^19.1.1"