feat(device-sim): 优化环境配置新增弹窗用户体验

- MQTT 账号密码设置默认值（mqtt@cmdb / mqtt@webpassw0RD）
- 主题配置移至高级选项折叠面板，简化表单布局
- 优化表单字段顺序，突出核心配置项
- 新增折叠面板样式，提升用户体验
Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/views/device-sim/EnvConfig.vue

@@ -73,8 +73,8 @@
             </el-form-item>
           </el-col>
           <el-col :span="12">
-            <el-form-item label="主题基础前缀" prop="topicPrefix">
-              <el-input v-model="form.topicPrefix" placeholder="如：device" @input="onBasePrefixChange" />
+            <el-form-item label="客户端 ID 前缀">
+              <el-input v-model="form.clientIdPrefix" placeholder="如：sim" />
             </el-form-item>
           </el-col>
         </el-row>
@@ -93,18 +93,22 @@
         <el-row :gutter="20">
           <el-col :span="12">
             <el-form-item label="用户名">
-              <el-input v-model="form.username" placeholder="MQTT 用户名" />
+              <el-input v-model="form.username" placeholder="MQTT 用户名（默认已填）" />
             </el-form-item>
           </el-col>
           <el-col :span="12">
             <el-form-item label="密码">
-              <el-input v-model="form.password" type="password" show-password placeholder="MQTT 密码" />
+              <el-input v-model="form.password" type="password" show-password placeholder="MQTT 密码（默认已填）" />
             </el-form-item>
           </el-col>
         </el-row>
 
-        <!-- 多主题配置 -->
-        <el-divider content-position="left">主题配置（按设备类型）</el-divider>
+        <!-- 高级选项：主题配置（折叠显示） -->
+        <el-collapse v-model="advancedCollapse" class="advanced-collapse">
+          <el-collapse-item title="高级选项（主题配置）" name="topics">
+            <el-form-item label="主题基础前缀" prop="topicPrefix">
+              <el-input v-model="form.topicPrefix" placeholder="如：device" @input="onBasePrefixChange" />
+            </el-form-item>
             <div class="topics-editor">
               <div class="topic-item" v-for="dt in deviceTypes" :key="dt">
                 <span class="topic-label">{{ deviceTypeLabel(dt) }}</span>
@@ -121,19 +125,15 @@
                 修改基础前缀可批量重置各设备主题；也可单独自定义每个设备类型的主题路径
               </el-tag>
             </div>
-
             <el-row :gutter="20" style="margin-top: 12px">
-          <el-col :span="12">
-            <el-form-item label="客户端 ID 前缀">
-              <el-input v-model="form.clientIdPrefix" placeholder="如：sim" />
-            </el-form-item>
-          </el-col>
               <el-col :span="12">
                 <el-form-item label="TLS 加密">
                   <el-switch v-model="form.useTls" />
                 </el-form-item>
               </el-col>
             </el-row>
+          </el-collapse-item>
+        </el-collapse>
       </el-form>
       <template #footer>
         <el-button @click="dialogVisible = false">取消</el-button>
@@ -177,6 +177,7 @@ const isEdit = ref(false)
 const saving = ref(false)
 const editId = ref('')
 const formRef = ref()
+const advancedCollapse = ref<string[]>([])  // 高级选项折叠面板状态（默认收起）
 
 /** 根据基础前缀生成默认多主题映射 */
 function buildDefaultTopics(prefix?: string | null): Record<string, string> {
@@ -192,8 +193,8 @@ const defaultForm = (): EnvConfigCreate => ({
   name: '',
   brokerHost: '',
   brokerPort: 1883,
-  username: '',
-  password: '',
+  username: 'mqtt@cmdb',
+  password: 'mqtt@webpassw0RD',
   topicPrefix: 'device',
   topics: buildDefaultTopics('device'),
   useTls: false,
@@ -383,6 +384,28 @@ onMounted(() => {
   font-size: 13px;
 }
 
+.advanced-collapse {
+  margin-top: 16px;
+  border: none;
+}
+
+.advanced-collapse :deep(.el-collapse-item__header) {
+  background: #f5f7fa;
+  border: 1px solid #ebeef5;
+  border-radius: 4px;
+  padding: 0 16px;
+  font-size: 14px;
+  color: #606266;
+}
+
+.advanced-collapse :deep(.el-collapse-item__wrap) {
+  border: none;
+}
+
+.advanced-collapse :deep(.el-collapse-item__content) {
+  padding-top: 16px;
+}
+
 .topics-editor {
   display: flex;
   flex-direction: column;
@@ -391,6 +414,7 @@ onMounted(() => {
   background: #fafafa;
   border-radius: 6px;
   border: 1px solid #ebeef5;
+  margin-top: 8px;
 }
 
 .topic-item {