fix(school): 修复搜索框重复显示两个搜索图标

- 移除 a-input-search 的 #prefix 插槽（组件自带搜索按钮）
- 涉及：课程管理、教师/学生/家长/班级管理

Made-with: Cursor

reading-platform-frontend/src/views/school/classes/ClassListView.vue

@@ -29,11 +29,7 @@
     <div class="action-bar">
       <div class="search-box">
         <a-input-search v-model:value="searchKeyword" placeholder="搜索班级名称" style="width: 250px;" @search="handleSearch"
-          allow-clear>
-          <template #prefix>
-            <SearchOutlined style="color: #B2BEC3;" />
-          </template>
-        </a-input-search>
+          allow-clear />
       </div>
       <a-button type="primary" class="add-btn" @click="showAddModal">
         <PlusOutlined class="btn-icon" />
@@ -302,7 +298,6 @@ import {
   HomeOutlined,
   BankOutlined,
   PlusOutlined,
-  SearchOutlined,
   EditOutlined,
   DeleteOutlined,
   TeamOutlined,

reading-platform-frontend/src/views/school/courses/CourseListView.vue

@@ -186,7 +186,6 @@
 import { ref, reactive, computed, onMounted } from 'vue';
 import { useRouter } from 'vue-router';
 import {
-  SearchOutlined,
   BookOutlined,
   ReadOutlined,
   StarFilled,

reading-platform-frontend/src/views/school/parents/ParentListView.vue

@@ -29,11 +29,7 @@
     <div class="action-bar">
       <div class="search-box">
         <a-input-search v-model:value="searchKeyword" placeholder="搜索家长姓名/手机号/账号" style="width: 280px;"
-          @search="handleSearch" allow-clear>
-          <template #prefix>
-            <SearchOutlined style="color: #B2BEC3;" />
-          </template>
-        </a-input-search>
+          @search="handleSearch" allow-clear />
       </div>
       <a-button type="primary" class="add-btn" @click="showAddModal">
         <PlusOutlined class="btn-icon" />
@@ -305,7 +301,6 @@
 <script setup lang="ts">
 import { ref, reactive, computed, onMounted } from 'vue';
 import {
-  SearchOutlined,
   IdcardOutlined,
   PlusOutlined,
   PhoneOutlined,

reading-platform-frontend/src/views/school/students/StudentListView.vue

@@ -45,11 +45,7 @@
           </a-select-option>
         </a-select>
         <a-input-search v-model:value="searchKeyword" placeholder="搜索学生姓名/家长" style="width: 220px;"
-          @search="handleSearch" allow-clear>
-          <template #prefix>
-            <SearchOutlined style="color: #B2BEC3;" />
-          </template>
-        </a-input-search>
+          @search="handleSearch" allow-clear />
       </div>
       <div class="actions">
         <a-button class="import-btn" @click="showImportModal">
@@ -314,7 +310,6 @@
 <script setup lang="ts">
 import { ref, reactive, computed, onMounted } from 'vue';
 import {
-  SearchOutlined,
   TeamOutlined,
   UserOutlined,
   EditOutlined,

reading-platform-frontend/src/views/school/teachers/TeacherListView.vue

@@ -29,11 +29,7 @@
     <div class="action-bar">
       <div class="search-box">
         <a-input-search v-model:value="searchKeyword" placeholder="搜索教师姓名/手机号/账号" style="width: 280px;"
-          @search="handleSearch" allow-clear>
-          <template #prefix>
-            <SearchOutlined style="color: #B2BEC3;" />
-          </template>
-        </a-input-search>
+          @search="handleSearch" allow-clear />
       </div>
       <a-button type="primary" class="add-btn" @click="showAddModal">
         <PlusOutlined class="btn-icon" />
@@ -206,7 +202,6 @@
 <script setup lang="ts">
 import { ref, reactive, computed, onMounted } from 'vue';
 import {
-  SearchOutlined,
   SolutionOutlined,
   PlusOutlined,
   PhoneOutlined,