feat(v2): add Top10 selection with soft group diversity, hard 10-item cap

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

logic/diversity.js

@@ -0,0 +1,34 @@
+function selectTop(scored, topN, config) {
+  const eligible = scored.filter((item) => !item.excludedFromTop10);
+  const excluded = scored.filter((item) => item.excludedFromTop10);
+
+  const sorted = [...eligible].sort((a, b) => b.score - a.score);
+
+  const groupCap = Math.max(1, Math.ceil(topN * 0.5));
+  const groupCounts = {};
+  const firstPass = [];
+  const deferred = [];
+
+  for (const item of sorted) {
+    const count = groupCounts[item.group] || 0;
+    if (count < groupCap && firstPass.length < topN) {
+      firstPass.push(item);
+      groupCounts[item.group] = count + 1;
+    } else {
+      deferred.push(item);
+    }
+  }
+
+  let selected = firstPass;
+  if (selected.length < topN) {
+    selected = selected.concat(deferred.slice(0, topN - selected.length));
+  }
+  selected = selected.slice(0, topN);
+
+  const selectedIds = new Set(selected.map((item) => item.ticket.id));
+  const notSelected = sorted.filter((item) => !selectedIds.has(item.ticket.id));
+
+  return { selected, excluded: excluded.concat(notSelected) };
+}
+
+module.exports = { selectTop };