feat(visualize): scale node size by degree (sqrt) so hubs read big

The old radius capped at degree ~17, so every well-connected node looked
the same size. Use 3.5 + sqrt(degree)*2.1 (clamped) → the heavily-linked
hubs (anthropic, agentic-systems, claude-code …) clearly stand out while
leaves stay small, giving the nebula a visible importance hierarchy.

Author: KylinMountain

openkb/templates/graph.html

@@ -243,7 +243,7 @@
 // build working nodes/edges from GRAPH (object-form edges: e.source/e.target)
 const nodes = GRAPH.nodes.map(n => ({
   ...n, x:0, y:0, z:0, vx:0, vy:0, vz:0,
-  r: 3.5 + Math.min(7, ((n.in || 0) + (n.out || 0)) * 0.42),   // small crisp nodes, scaled by degree
+  r: 3.5 + Math.min(18, Math.sqrt((n.in || 0) + (n.out || 0)) * 2.1),   // sqrt-scaled by degree → hubs read big, leaves stay small
   col: colorOf(n.type),                               // cached color → no per-frame lookup
   alpha: 1,                                            // per-node fade (legend toggle)
   sx:0, sy:0, rz:0, pp:1, hl:1, pinned:false           // projection cache + smoothed highlight + pinned (drag to pull out)