fix: referral network rendering — portal fix and visual tuning

Portal to document.body escapes main's contain:content which broke
fixed positioning (container had height:0 and was clipped to main).

Visual fixes for 662+ node graphs:
- labels only on large nodes (threshold 6→14, density 0.5→0.12)
- leaf nodes 5px, referrers 10px, campaigns 16px
- edge opacity reduced to prevent white starburst
- default edge color opacity lowered

src/pages/ReferralNetwork/utils.ts

@@ -46,8 +46,7 @@ export function getUserNodeColor(
  * Size is proportional to direct_referrals, clamped between min and max.
  */
 export function getUserNodeSize(directReferrals: number): number {
-  const MIN_SIZE = 12;
-  const MAX_SIZE = 50;
-  if (directReferrals === 0) return MIN_SIZE;
-  return Math.min(MAX_SIZE, MIN_SIZE + Math.sqrt(directReferrals) * 5);
+  if (directReferrals === 0) return 5;
+  if (directReferrals <= 2) return 10;
+  return Math.min(40, 10 + Math.sqrt(directReferrals) * 4);
 }