Show downline count and downline POL on matrix positions

Each tree node now carries a rollup of its subtree — members below and
their combined earned POL — shown as a footer line on pyramid cards and
inline in the list view.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

chain.js

@@ -387,6 +387,12 @@ function getMatrixTree() {
     };
     n.left = node(m.l, depth + 1);
     n.right = node(m.r, depth + 1);
+    // downline rollup: members below this position and the POL they earned
+    n.downCount = 0; n.downPol = 0;
+    for (const c of [n.left, n.right]) if (c && !c.missing) {
+      n.downCount += 1 + (c.downCount || 0);
+      n.downPol = +(n.downPol + (c.earnedPol || 0) + (c.downPol || 0)).toFixed(2);
+    }
     return n;
   }
   const root = node(1, 0);