fix(growth): rank the rate board by a smoothed score

Show the real percentage on the card, but sort with delta / (baseline + prior) so a small baseline cannot dominate. Same-day publishes stay off the rate board.

reaction_board/web/static/format.js

@@ -46,6 +46,12 @@ export function formatPercent(value, digits = 2) {
   return `${(Number(value) * 100).toFixed(digits)}%`;
 }
 
+export function formatSignedPercent(value, digits = 2) {
+  const text = formatPercent(value, digits);
+  if (text === "—" || Number(value) <= 0) return text;
+  return `+${text}`;
+}
+
 export function formatDate(timestamp) {
   if (!timestamp) return "—";
   const date = new Date(Number(timestamp) * 1000);