Add Graph Narrative Generator - autonomous natural-language graph reports

New interactive tool (docs/narrative.html) that analyzes any graph and generates
comprehensive written narratives covering:

- Structural overview (density, diameter, clustering, components)
- Key player analysis (degree, betweenness, PageRank, closeness centrality)
- Community detection via label propagation
- Vulnerability assessment (articulation points, bridges)
- Anomaly detection (z-score outliers)
- Model comparison (small-world coefficient)
- Growth forecasting (preferential attachment analysis)
- Actionable recommendations

Features:
- 5 narrative tones: Analyst, Storyteller, Detective, Advisor, Journalist
- 8 configurable analysis modules
- 3 depth levels (brief/standard/detailed)
- 8 graph presets including Karate Club and Small World
- Auto-Narrator mode: autonomous iterative discovery (triangles, assortativity)
- Force-directed Canvas visualization with community coloring
- Export to Markdown, HTML, JSON, or plain text
- Edge list and adjacency list input formats

Usage: Open docs/narrative.html, load a preset or enter edges, select tone and modules, click Generate.

Author: sauravbhattacharya001

docs/index.html

@@ -59,6 +59,7 @@ <h2>GraphVisual</h2>
         <a href="epidemic.html" class="sidebar-link"><span class="icon">🏥</span>Epidemic Sim</a>
         <a href="graph-automaton.html" class="sidebar-link"><span class="icon">🤖</span>Graph Automaton</a>
         <a href="gnn-playground.html" class="sidebar-link"><span class="icon">🧠</span>GNN Playground</a>
+        <a href="narrative.html" class="sidebar-link"><span class="icon">📝</span>Narrative Gen</a>
     </div>
     <div class="sidebar-section">
         <div class="sidebar-section-title">Architecture</div>