feat: add ai-workflow-builder demo (React)

[Geliogabalus]

Summary

• Adds a new ai-workflow-builder/react demo: a JointJS+ for React AI agent/workflow builder with agent, tool, skill, and output nodes, an inspector panel, run controls, and export.
• Registers the demo in demos.config.json with the react variant.

Test plan

• npm install and npm run dev inside ai-workflow-editor/react and confirm the canvas loads with the sample workflow
• Verify node inspector, connections, and run/export controls work as expected