Improve graph node visualization and interaction

- Replace circular nodes with clean rectangular 'Monopoly-style' cards
- Add colored title bars showing node types (EPIC, TASK, FEATURE, etc.)
- Improve text sizing and readability with larger fonts
- Implement NodeDetailsModal for viewing complete node information
- Add 'View Details' option to node context menu
- Adjust force simulation parameters for better node positioning
- Increase minimum edge distances and reduce aggressive forces
- Remove duplicate node title rendering issues

Features:
- Clean rectangular nodes with colored headers
- Better spaced layout with gentler physics simulation
- Full node details modal with complete descriptions and metadata
- Improved user interaction flow from viewing to editing

Author: mvalancy