Add comprehensive centrality analysis to slipnet study

Key finding: Eccentricity is the only metric significantly correlated
with conceptual depth (r=-0.380, p=0.029). Local centrality measures
(degree, betweenness, closeness) show no significant correlation.

New files:
- compute_centrality.py: Computes 8 graph metrics
- centrality_comparison.png: Visual comparison of all metrics
- Updated paper with full analysis

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

slipnet_analysis/centrality_results.json

@@ -0,0 +1,86 @@
+{
+  "analysis_type": "centrality_correlation",
+  "n_nodes": 33,
+  "metrics": [
+    {
+      "name": "Eccentricity",
+      "key": "eccentricity",
+      "pearson_r": -0.3796,
+      "pearson_p": 0.029349,
+      "spearman_r": -0.2988,
+      "spearman_p": 0.091181,
+      "r_squared": 0.1441,
+      "significant": true
+    },
+    {
+      "name": "Closeness Centrality",
+      "key": "closeness",
+      "pearson_r": -0.2699,
+      "pearson_p": 0.128801,
+      "spearman_r": -0.1804,
+      "spearman_p": 0.315126,
+      "r_squared": 0.0728,
+      "significant": false
+    },
+    {
+      "name": "Degree Centrality",
+      "key": "degree",
+      "pearson_r": -0.2643,
+      "pearson_p": 0.137147,
+      "spearman_r": -0.2362,
+      "spearman_p": 0.18565,
+      "r_squared": 0.0699,
+      "significant": false
+    },
+    {
+      "name": "PageRank",
+      "key": "pagerank",
+      "pearson_r": -0.257,
+      "pearson_p": 0.148771,
+      "spearman_r": -0.1908,
+      "spearman_p": 0.287516,
+      "r_squared": 0.0661,
+      "significant": false
+    },
+    {
+      "name": "Clustering Coefficient",
+      "key": "clustering",
+      "pearson_r": -0.2191,
+      "pearson_p": 0.2205,
+      "spearman_r": -0.2761,
+      "spearman_p": 0.119934,
+      "r_squared": 0.048,
+      "significant": false
+    },
+    {
+      "name": "Betweenness Centrality",
+      "key": "betweenness",
+      "pearson_r": -0.1716,
+      "pearson_p": 0.339655,
+      "spearman_r": -0.0801,
+      "spearman_p": 0.657858,
+      "r_squared": 0.0294,
+      "significant": false
+    },
+    {
+      "name": "Eigenvector Centrality",
+      "key": "eigenvector",
+      "pearson_r": -0.1482,
+      "pearson_p": 0.410425,
+      "spearman_r": -0.2367,
+      "spearman_p": 0.184728,
+      "r_squared": 0.022,
+      "significant": false
+    },
+    {
+      "name": "Avg Neighbor Degree",
+      "key": "avg_neighbor_degree",
+      "pearson_r": 0.0517,
+      "pearson_p": 0.775231,
+      "spearman_r": -0.3006,
+      "spearman_p": 0.089172,
+      "r_squared": 0.0027,
+      "significant": false
+    }
+  ]
+}