fix: add fill border to node-border program config

The createNodeBorderProgram was missing the second border entry
with { size: { fill: true }, color: { attribute: 'color' } }
which renders the node's fill color. Without it, node bodies
were transparent and only edges were visible.

src/pages/ReferralNetwork/components/NetworkGraph.tsx

@@ -127,6 +127,10 @@ const BorderedNodeProgram = createNodeBorderProgram({
       size: { attribute: 'borderSize', defaultValue: 0 },
       color: { attribute: 'borderColor' },
     },
+    {
+      size: { fill: true },
+      color: { attribute: 'color' },
+    },
   ],
 });