Add Graph Tournament Bracket - interactive centrality-based node tournament

New interactive HTML tool (docs/tournament.html) where graph nodes compete
head-to-head based on centrality metrics in tournament brackets.

Features:
- 7 graph presets (Petersen, K5, Cycle, Star, Binary Tree, Grid, Random)
- 4 metrics: Degree, Closeness, Betweenness centrality, PageRank
- Single Elimination mode with animated Canvas bracket visualization
- Round Robin mode with standings table and medal podium
- Step-through or auto-play with 800ms intervals
- Proactive insights: upset detection, dominance analysis, seeding recommendations
- Seed-based matchups with underperformer flagging

Usage: Open docs/tournament.html, select a graph and metric, click Start.

Author: sauravbhattacharya001