fix: improve graph spacing, mobile layout, and Telegram viewport

- Increase FA2 scalingRatio to 10 and decrease gravity to 0.5 for
  better node spacing (less cluttered graph)
- Use 100dvh instead of 100vh for Telegram Mini App viewport compat
- Hide legend on mobile to prevent overlay collision
- Move controls to bottom-right on mobile, bottom-center on desktop
- Make stats single-column on mobile for compact layout

src/pages/ReferralNetwork/components/NetworkGraph.tsx

@@ -236,9 +236,10 @@ export function NetworkGraph({ data, className }: NetworkGraphProps) {
     if (graph.order > 0) {
       const supervisor = new FA2LayoutSupervisor(graph, {
         settings: {
-          gravity: 1,
-          scalingRatio: 2,
+          gravity: 0.5,
+          scalingRatio: 10,
           barnesHutOptimize: true,
+          slowDown: 2,
         },
       });
       fa2Ref.current = supervisor;