Add GenerateVideoNode for video generation using Replicate and fal.ai:
- Add GenerateVideoNodeData interface with video output field
- Add generateVideo to NodeType union
- Create GenerateVideoNode component with provider/model selection
- Register in WorkflowCanvas with purple minimap color (#9333ea)
- Add default dimensions and node data creation in store
- Update validation.ts for new node type
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>