Phase 3.1: Interactive Network Visualization

Features:
- Force-directed graph with react-force-graph-2d
- Color-coded nodes (COG/Capability/Requirement/Vulnerability)
- Interactive controls (zoom, pan, node selection)
- 'What if?' simulation mode
- PNG export functionality
- Node highlighting and info panel
- Network statistics overlay

Perfect for visualizing COG hierarchies and analyzing single points of failure.