feat(course): 岗位选择器添加全选按钮

- 在选择岗位弹窗中添加全选/取消全选功能
- 支持对当前筛选结果进行全选操作

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/views/manager/edit-course.vue

@@ -552,6 +552,13 @@
               <el-icon><Search /></el-icon>
             </template>
           </el-input>
+          <el-button 
+            type="primary" 
+            :plain="!isAllSelected"
+            @click="toggleSelectAll"
+          >
+            {{ isAllSelected ? '取消全选' : '全选' }}
+          </el-button>
         </div>
         
         <div class="available-positions">
@@ -719,6 +726,30 @@ const filteredAvailablePositions = computed(() => {
   return filtered
 })
 
+// 是否全选
+const isAllSelected = computed(() => {
+  if (filteredAvailablePositions.value.length === 0) return false
+  return filteredAvailablePositions.value.every(
+    (p: any) => selectedPositions.value.includes(p.id)
+  )
+})
+
+// 全选/取消全选
+const toggleSelectAll = () => {
+  if (isAllSelected.value) {
+    // 取消全选：移除当前筛选结果中的所有岗位
+    const filteredIds = filteredAvailablePositions.value.map((p: any) => p.id)
+    selectedPositions.value = selectedPositions.value.filter(
+      id => !filteredIds.includes(id)
+    )
+  } else {
+    // 全选：添加当前筛选结果中的所有岗位
+    const filteredIds = filteredAvailablePositions.value.map((p: any) => p.id)
+    const newSelection = new Set([...selectedPositions.value, ...filteredIds])
+    selectedPositions.value = Array.from(newSelection)
+  }
+}
+
 // 考试设置相关
 const examSettingsLoading = ref(false)
 const examSettings = reactive({
@@ -2920,6 +2951,9 @@ const loadAvailablePositions = async () => {
 // 岗位选择器样式
 .position-selector-content {
   .selector-header {
+    display: flex;
+    align-items: center;
+    gap: 12px;
     margin-bottom: 20px;
   }