Add workflow editor and node types support in frontend and backend

- Introduce a new workflow editor component for visualizing and managing workflows, allowing users to add nodes and define connections.
- Implement backend support for node types, including validation and constraints for workflow graphs.
- Add new API endpoints for retrieving node types and their specifications.
- Enhance the AssistantPage to integrate the workflow editor, enabling users to create and edit workflows directly.
- Update frontend components to support new workflow functionalities, including condition edges and generic nodes.
- Refactor existing code to accommodate the new workflow features and improve overall structure.

frontend/package.json

@@ -9,6 +9,7 @@
     "lint": "eslint"
   },
   "dependencies": {
+    "@xyflow/react": "^12.11.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "lucide-react": "^1.17.0",