feat: v1.4.0 - 典型方案采纳、推荐方案列表、审计字段、导航优化

- 添加典型方案采纳功能 (POST /api/plans/<id>/adopt)
- 添加推荐方案列表 (GET /api/students/<id>/recommended-plans)
- PracticePlan 新增 created_by/updated_by/updated_at 审计字段
- 方案编辑/详情页导航优化 (bfcache 处理、pageshow 事件)
- 方案列表支持删除功能
- 学员列表'暂无方案/问题'样式统一
- 更新文档：问题文件已废弃（迁移到数据库）
- 更新部署脚本和验证清单

app/templates/problems.html

@@ -189,6 +189,30 @@
 let allProblems = [];
 let currentEditId = null;
 let currentDeleteId = null;
+const PROBLEM_FILTER_KEY = 'problem_filters';
+
+function saveProblemFilterState() {
+    const state = {
+        search: document.getElementById('searchInput').value,
+        filterCategory: document.getElementById('filterCategory').value,
+        groupBy: document.getElementById('groupByCategory').value
+    };
+    sessionStorage.setItem(PROBLEM_FILTER_KEY, JSON.stringify(state));
+}
+
+function restoreProblemFilterState() {
+    const saved = sessionStorage.getItem(PROBLEM_FILTER_KEY);
+    if (!saved) return;
+    try {
+        const state = JSON.parse(saved);
+        if (state.search) document.getElementById('searchInput').value = state.search;
+        if (state.filterCategory) document.getElementById('filterCategory').value = state.filterCategory;
+        if (state.groupBy) document.getElementById('groupByCategory').value = state.groupBy;
+        saveProblemFilterState();
+    } catch (e) {
+        console.error('恢复问题筛选状态失败', e);
+    }
+}
 
 window.pageInit = function() {
     loadProblems();
@@ -199,10 +223,13 @@ window.pageInit = function() {
 async function loadProblems() {
     const response = await fetch('/api/problems');
     allProblems = await response.json();
+    restoreProblemFilterState();
     applyProblemFilters();
 }
 
 function applyProblemFilters() {
+    saveProblemFilterState();
+
     const search = document.getElementById('searchInput').value.toLowerCase();
     const filterCategory = document.getElementById('filterCategory').value;
     const groupBy = document.getElementById('groupByCategory').value;