feat: 支持单套试卷同一提交人多次刷卷并展示

- DataService::build 新增 aggregateByStudent 按学号聚合：
  dedupe=true 仅保留最新一份；false 则每学号一行（代表成绩取最高分）
  附 attempts(次数) 与 attempts_list(每次提交明细)，修正提交人数被多次提交inflate的问题
- api.php dashboard 透传 attempts/attempts_list；statOf 增加 attempts 求和；export 增加刷题次数列
- dashboard.php 成员榜加"刷N次"徽标，点击下钻弹窗看每次提交（时间/成绩/时长/暂存）；hero 显示总提交次数
- 主统计页成绩明细同样加"刷N次"徽标与下钻弹窗
- stats 新增 attempts_total

assets/app.js

@@ -447,10 +447,13 @@
       const sig = r.sid + '|' + r.score + '|' + r.submit_at;
       const changed = state.prevMap[r.sid] && state.prevMap[r.sid] !== sig;
       const isNew = r.sid && state.newSids.has(r.sid);
-      const clsName = (changed ? 'diff ' : '') + (isNew ? 'new' : '');
-      return '<tr class="' + clsName.trim() + '">' +
+      const canDrill = (r.attempts || 1) > 1;
+      const clsName = (changed ? 'diff ' : '') + (isNew ? 'new ' : '') + (canDrill ? 'clickable' : '');
+      const att = canDrill ? ' <span class="tag tag-att" title="查看 ' + r.attempts + ' 次提交明细">刷' + r.attempts + '次</span>' : '';
+      const onclk = canDrill ? ' onclick="openAttemptsModal(' + JSON.stringify(r.sid) + ')"' : '';
+      return '<tr class="' + clsName.trim() + '"' + onclk + '>' +
         '<td class="sid">' + esc(r.sid) + '</td>' +
-        '<td class="name">' + esc(r.name) + '</td>' +
+        '<td class="name">' + esc(r.name) + att + '</td>' +
         '<td>' + esc(r.cls || '') + '</td>' +
         '<td>' + esc(r.grp || '') + '</td>' +
         '<td class="score num ' + scoreClass(r.score) + '">' + (r.score == null ? '-' : r.score) + '</td>' +
@@ -499,6 +502,28 @@
       '</td><td class="num">' + esc(u.submit_at) + '</td></tr>').join('');
   }
 
+  /* 多次刷题下钻弹窗（主统计页成绩明细） */
+  function openAttemptsModal(sid) {
+    const r = (state.rows || []).find(x => String(x.sid) === String(sid));
+    if (!r || (r.attempts || 1) <= 1) return;
+    const list = r.attempts_list || [];
+    const rows = list.map(a => {
+      const sc = a.score == null ? '<span class="muted">未判分</span>' : esc(a.score);
+      const tmp = a.temp_save ? ' <span class="tag tag-gray">暂存</span>' : '';
+      return '<tr><td class="num">' + esc(a.submit_at) + '</td><td class="num">' + sc + tmp +
+        '</td><td class="num">' + esc(a.duration_txt || '-') + '</td></tr>';
+    }).join('');
+    $('#attTitle').textContent = (r.name || '') + ' · 共 ' + r.attempts + ' 次提交';
+    $('#attBody').innerHTML = list.length
+      ? '<table class="grid compact"><thead><tr><th>提交时间</th><th>成绩</th><th>考试时长</th></tr></thead><tbody>' + rows + '</tbody></table>'
+      : '<div class="empty">无提交明细</div>';
+    $('#attemptsModal').classList.add('open');
+  }
+  function closeAttemptsModal() {
+    const m = $('#attemptsModal');
+    if (m) m.classList.remove('open');
+  }
+
   /* ---------------- 自动刷新 ---------------- */
   function schedule() {
     if (state.timer) clearInterval(state.timer);