Implement the flowchart editor page with React Flow integration:
- Install reactflow package for canvas rendering
- Create editor page that fetches project data from Supabase
- Add loading state with spinner while fetching
- Handle unauthorized access and not found with appropriate responses
- Render React Flow canvas with grid background
- Add header with project name and back link to dashboard
- Initialize React Flow with nodes and edges from flowchart_data
- Add type converters for FlowchartNode/Edge to React Flow types
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>