fix: index.html mobile UI - wrap buttons and filters properly

- Split filters and action buttons into separate rows
- Use flex-wrap for mobile responsiveness
- Remove duplicate btn-group on student list page

app/templates/index.html

@@ -61,33 +61,34 @@
 {% block content %}
 <!-- 学员列表页面 -->
 <div id="studentListPage">
-    <div class="d-flex justify-content-between align-items-center mb-4">
+    <!-- 筛选条件行 -->
-        <div class="d-flex align-items-center gap-3">
+    <div class="d-flex flex-wrap gap-2 mb-3 align-items-center">
-            <h4><i class="bi bi-people"></i> 学员列表</h4>
+        <h4 class="me-2 mb-0"><i class="bi bi-people"></i> 学员列表</h4>
-            <select class="form-select form-select-sm" style="width:auto;" id="classFilter" onchange="loadStudents()">
+        <select class="form-select form-select-sm" style="width:auto; min-width:120px;" id="classFilter" onchange="loadStudents()">
             <option value="">全部班级</option>
         </select>
-            <input type="text" class="form-control form-control-sm" style="width:150px;" placeholder="搜索姓名..." id="nameFilter" oninput="loadStudents()">
+        <input type="text" class="form-control form-control-sm" style="width:120px;" placeholder="姓名..." id="nameFilter" oninput="loadStudents()">
         <button class="btn btn-primary btn-sm active" id="mineStudentFilterBtn" onclick="toggleMineStudentFilter()">
             <i class="bi bi-person"></i> 我的
         </button>
     </div>
-        <div class="btn-group">
+
-            <button class="btn btn-outline-secondary" onclick="downloadTemplate()">
+    <!-- 操作按钮行 -->
+    <div class="d-flex flex-wrap gap-2 mb-3">
+        <button class="btn btn-outline-secondary btn-sm" onclick="downloadTemplate()">
             <i class="bi bi-download"></i> 模板下载
         </button>
-            <button class="btn btn-outline-primary" onclick="document.getElementById('importFileInput').click()">
+        <button class="btn btn-outline-primary btn-sm" onclick="document.getElementById('importFileInput').click()">
             <i class="bi bi-upload"></i> CSV导入
         </button>
         <input type="file" id="importFileInput" accept=".csv" style="display:none" onchange="importStudents(this)">
-            <button class="btn btn-outline-success" onclick="exportStudents()">
+        <button class="btn btn-outline-success btn-sm" onclick="exportStudents()">
-                <i class="bi bi-file-earmark-arrow-up"></i> 导出学员
+            <i class="bi bi-file-arrow-up"></i> 导出
         </button>
-            <button class="btn btn-primary" onclick="showAddStudentModal()">
+        <button class="btn btn-primary btn-sm" onclick="showAddStudentModal()">
             <i class="bi bi-plus-lg"></i> 新增学员
         </button>
     </div>
-    </div>
 
     <div class="row" id="studentList">
         <!-- 学员卡片将通过JS动态加载 -->