feat: wire computeKpis into the page render (#5)

src/services/player-service.js

@@ -292,10 +292,30 @@ async function refreshAllPlayersInDB(progressCallback = null) {
   }
 }
 
+/**
+ * Aggregates KPI summary stats from an already-fetched player array.
+ * All fields are derived from the player list — no extra DB queries.
+ */
+function computeKpis(players) {
+  const active = players.filter(p => p.rating != null && p.rating > 0);
+  const avg = active.length > 0
+    ? Math.round(active.reduce((sum, p) => sum + p.rating, 0) / active.length)
+    : null;
+
+  return {
+    tracked: players.length,
+    active: active.length,
+    avg,
+    climbing: players.filter(p => p.ratingChange != null && p.ratingChange > 0).length,
+    slipping: players.filter(p => p.ratingChange != null && p.ratingChange < 0).length
+  };
+}
+
 module.exports = {
   getPlayerDataFromDB,
   scrapePDGARating,
   getPredictedRatingFromDB,
   getAllRatingsFromDB,
-  refreshAllPlayersInDB
+  refreshAllPlayersInDB,
+  computeKpis
 };