Add Community Evolution Tracker - interactive community lifecycle visualization

New interactive tool (docs/community-evolution.html) that tracks how graph
communities evolve over time with autonomous event detection:

- 4 presets: City Districts, Social Network, Supply Chain, Random Evolution
- Greedy modularity-based community detection with color-coded visualization
- Force-directed layout with community attraction
- Play/pause/step timeline with full history navigation
- Autonomous event detection: births, deaths, merges, splits, growth, shrinkage
- Proactive insights: fragile community warnings, merger candidates, drifting nodes
- Real-time analytics: community count, modularity score, largest community charts

Usage: Open docs/community-evolution.html, select a preset, click Generate, then
press Play to watch communities evolve. Step through time or adjust edge add/remove
rates to explore different dynamics.

Author: sauravbhattacharya001