Fix author network graph: tune force sim, reduce node count

- Raise co-authorship threshold from 1 to 2 shared drafts (498→156 nodes)
- Tune D3 force parameters for large graphs: capped link strength,
  wider distance, adaptive charge, lower velocity decay
- Add initial circular layout to prevent explosion on load
- Fix cluster highlighting with fallback name matching and
  position validation before zoom-to-fit

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/webui/data.py

@@ -508,18 +508,18 @@ def get_author_network_full(db: Database) -> dict:
             "org": aff, "draft_count": cnt, "drafts": drafts, "avg_score": avg
         }
 
-    # Build node set: authors with 2+ drafts OR 1+ co-authorship
+    # Build node set: authors with meaningful collaboration (2+ shared drafts)
     node_set = set()
     edges = []
     for a, b, shared in pairs:
-        if shared >= 1:
+        if shared >= 2:
             node_set.add(a)
             node_set.add(b)
             edges.append({"source": a, "target": b, "weight": shared})
 
-    # Also include authors with 2+ drafts even if no co-authorships
+    # Also include authors with 3+ drafts even if no co-authorships
     for name, info in author_info.items():
-        if info["draft_count"] >= 2:
+        if info["draft_count"] >= 3:
             node_set.add(name)
 
     nodes = []