feat: 文件夹双策略识别 + 布局选项 + 移除提交率卡片 + localStorage缓存层

- 文件夹识别：mode 含 'folder' 优先，缺省时用 parentId 引用反推；
  即使卷王版本无 mode 字段也能正确分组，避免'直接没有文件夹选项'
- 布局选项：工具栏新增 #layoutSel（默认 / 成绩明细与缺考名单同行），
  用 CSS Grid 双模式渲染，窄屏回落单列；偏好写 localStorage
- 移除统计卡片中的提交率卡片（卡片数 9 → 8）
- localStorage 缓存层：问卷列表 / 每个项目数据 / 看板数据 / 班级组别
  筛选 / 布局 / 上次项目 id 全部持久化；进入页面先渲染缓存，
  后台再异步拉新数据并写回缓存；网络失败时仍能用本地缓存查看
- dashboard.php 同步：文件夹识别 / 数据缓存一致更新

dashboard.php

@@ -87,6 +87,15 @@ function rateColor(r){
   return 'var(--danger)';
 }
 
+/* 本地存储（缓存问卷列表/看板数据，重开即恢复） */
+const LS = {
+  get(k, def){ try { const v = localStorage.getItem(k); return v == null ? def : JSON.parse(v); } catch(e){ return def; } },
+  set(k, v){ try { localStorage.setItem(k, JSON.stringify(v)); } catch(e){} },
+  del(k){ try { localStorage.removeItem(k); } catch(e){} }
+};
+const LS_PROJECTS = 'ny_projects';
+const LS_DASH = pid => 'ny_dashboard_' + pid;
+
 let DASH = null;   // 最近一次看板数据
 let CUR  = null;   // 当前查看的班级名
 
@@ -102,16 +111,60 @@ async function api(action, opts){
   throw new Error((j && (j.msg || j.error)) || '请求失败');
 }
 
+/* ---------- 问卷列表：双策略识别文件夹 + 缓存优先 ---------- */
+function renderProjects(list){
+  const sel = $('#projectSel');
+  const keep = sel.value;
+  sel.innerHTML = '<option value="">请选择问卷 / 考试</option>';
+  // 双策略识别文件夹：mode 含 folder，或被其他项目作为 parent_id 引用
+  const isFolder = p => (p.mode || '').toLowerCase().includes('folder');
+  const parentIds = new Set();
+  list.forEach(p => { const pid = (p.parent_id || '0'); if (pid && pid !== '0' && pid !== '') parentIds.add(pid); });
+  const folderSet = new Set();
+  list.forEach(p => { if (isFolder(p) || parentIds.has(p.id)) folderSet.add(p.id); });
+  const childOf = fid => list.filter(p => !folderSet.has(p.id) && (p.parent_id || '0') === fid);
+
+  // 根项
+  list.filter(p => !folderSet.has(p.id)).forEach(p => {
+    const o = document.createElement('option');
+    o.value = p.id; o.textContent = (p.mode ? '[' + p.mode + '] ' : '') + p.name + '（' + (p.total || 0) + '份）';
+    sel.appendChild(o);
+  });
+  // 文件夹
+  list.filter(p => folderSet.has(p.id)).forEach(f => {
+    const kids = childOf(f.id);
+    if (!kids.length) return;
+    const og = document.createElement('optgroup');
+    og.label = '📁 ' + f.name;
+    kids.forEach(p => {
+      const o = document.createElement('option');
+      o.value = p.id; o.textContent = (p.mode ? '[' + p.mode + '] ' : '') + p.name + '（' + (p.total || 0) + '份）';
+      og.appendChild(o);
+    });
+    sel.appendChild(og);
+  });
+  if (keep && list.some(p => p.id === keep)) sel.value = keep;
+  else {
+    const last = LS.get('ny_dash_last_pid', '');
+    if (last && list.some(p => p.id === last)) sel.value = last;
+  }
+}
+
 async function loadProjects(){
+  // 1) 先读本地缓存
+  const cached = LS.get(LS_PROJECTS, []);
+  if (Array.isArray(cached) && cached.length) {
+    renderProjects(cached);
+  }
+  // 2) 后台异步刷新
   try {
     const list = await api('projects');
-    const sel = $('#projectSel');
-    const keep = sel.value;
-    sel.innerHTML = '<option value="">请选择问卷 / 考试</option>' +
-      list.map(p => '<option value="' + esc(p.id) + '">' + esc(p.name) + '（' + esc(p.mode || '') + '）</option>').join('');
-    if (keep) sel.value = keep;
+    LS.set(LS_PROJECTS, list || []);
+    renderProjects(list || []);
   } catch (e) {
-    $('#classGrid').innerHTML = '<div class="empty">加载问卷列表失败：' + esc(e.message) + '</div>';
+    if (!cached || !cached.length) {
+      $('#classGrid').innerHTML = '<div class="empty">加载问卷列表失败：' + esc(e.message) + '</div>';
+    }
   }
 }
 
@@ -241,20 +294,39 @@ async function loadDashboard(){
     $('#classGrid').innerHTML = '<div class="empty">请选择问卷 / 考试以查看各班数据</div>';
     return;
   }
+
+  // 1) 缓存优先：先渲染上次保存的看板，避免空白
+  const cached = LS.get(LS_DASH(pid), null);
+  if (cached && cached.classes) {
+    DASH = cached;
+    renderSummary(DASH);
+    renderClasses(DASH);
+    $('#lastUpdate').textContent = (cached.updated_at || '—') + '（缓存）';
+    if (CUR) {
+      const still = (DASH.classes || []).some(x => x.class === CUR);
+      if (still) showClassDetail(CUR); else backToOverview();
+    }
+  }
+
+  // 2) 后台拉真实数据
   try {
-    DASH = await api('dashboard', { params: { projectId: pid } });
+    const fresh = await api('dashboard', { params: { projectId: pid } });
+    DASH = fresh;
+    LS.set(LS_DASH(pid), fresh);
+    LS.set('ny_dash_last_pid', pid);
     renderSummary(DASH);
     renderClasses(DASH);
     $('#lastUpdate').textContent = DASH.updated_at || '-';
     $('#liveDot').classList.add('on');
     setTimeout(() => $('#liveDot').classList.remove('on'), 900);
-    // 若正在看某班详情，刷新后同步更新
     if (CUR) {
       const still = (DASH.classes || []).some(x => x.class === CUR);
       if (still) showClassDetail(CUR); else backToOverview();
     }
   } catch (e) {
-    $('#classGrid').innerHTML = '<div class="empty">数据加载失败：' + esc(e.message) + '</div>';
+    if (!cached) {
+      $('#classGrid').innerHTML = '<div class="empty">数据加载失败：' + esc(e.message) + '</div>';
+    }
   }
 }