style(frontend): Vue 模板占位符 JSON 示例引号转义（lint 合规）

- DeviceList.vue: 运行时参数 JSON 示例占位符转义
- ApiCaseList.vue: 请求体 JSON 示例占位符转义
- ApiPresetDialog.vue: headers/body/bodyTemplate 示例占位符转义
- TaskList.vue: 请求头/CSV 映射/步骤占位符 JSON 示例统一转义
Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/components/device/DeviceList.vue

@@ -282,7 +282,7 @@
             v-model="reportForm.payloadStr"
             type="textarea"
             :rows="6"
-            placeholder='如：{"status": "online", "battery": 85}'
+            placeholder="如：{"status": "online", "battery": 85}"
           />
         </el-form-item>
       </el-form>

frontend/src/views/api-test/ApiCaseList.vue

@@ -279,11 +279,11 @@
             v-model="apiConfig.bodyText"
             type="textarea"
             :rows="8"
-            placeholder='{
-  "messageName": "测试会议_{__RANDOM_NAME_8__}",
-  "startTime": "{__NOW__}",
-  "endTime": "{__NOW_+2_H__}"
-}'
+            placeholder="{
+  "messageName": "测试会议_{__RANDOM_NAME_8__}",
+  "startTime": "{__NOW__}",
+  "endTime": "{__NOW_+2_H__}"
+}"
             style="font-family: 'Courier New', monospace; font-size: 12px;"
           />
         </el-form-item>

frontend/src/views/performance/ApiPresetDialog.vue

@@ -47,7 +47,7 @@
               v-model="form.headers"
               type="textarea"
               :rows="3"
-              placeholder='{"Content-Type": "application/json"}'
+              placeholder="{"Content-Type": "application/json"}"
             />
           </el-form-item>
         </el-col>
@@ -68,7 +68,7 @@
               v-model="form.body"
               type="textarea"
               :rows="4"
-              placeholder='{"key": "value"}'
+              placeholder="{&quot;key&quot;: &quot;value&quot;}"
             />
           </el-form-item>
         </el-col>
@@ -78,7 +78,7 @@
               v-model="form.bodyTemplate"
               type="textarea"
               :rows="4"
-              placeholder='{"__NOW__": "datetime", "name": "会议名称"}'
+              placeholder="{&quot;__NOW__&quot;: &quot;datetime&quot;, &quot;name&quot;: &quot;会议名称&quot;}"
             />
           </el-form-item>
         </el-col>

frontend/src/views/performance/TaskList.vue

@@ -364,7 +364,7 @@
                 </el-form-item>
               </el-col>
               <el-col :span="16">
-                <el-input v-model="api.headers" type="textarea" :rows="1" placeholder='请求头（JSON），可选，如 {"Content-Type": "application/json"}' />
+                <el-input v-model="api.headers" type="textarea" :rows="1" placeholder="请求头（JSON），可选，如 {&quot;Content-Type&quot;: &quot;application/json&quot;}" />
               </el-col>
             </el-row>
             <el-input v-model="api.body" type="textarea" :rows="2" placeholder="请求体（JSON），可选" />
@@ -456,7 +456,7 @@
                 字段映射（JSON）
                 <FieldTip content="将 CSV 列映射到请求变量。key 为请求字段，value 用 {{csv.列名}} 引用，如 {&quot;username&quot;: &quot;{{csv.username}}&quot;}。登录接口将 username/password 映射到对应列即可实现多账号" />
               </template>
-              <el-input v-model="form.csvVariableMapping" type="textarea" :rows="2" placeholder='{"username": "{{csv.username}}", "password": "{{csv.password}}"}' />
+              <el-input v-model="form.csvVariableMapping" type="textarea" :rows="2" placeholder="{&quot;username&quot;: &quot;{{csv.username}}&quot;, &quot;password&quot;: &quot;{{csv.password}}&quot;}" />
             </el-form-item>
           </template>
         </template>
@@ -509,7 +509,7 @@
                   v-model="step.headersText"
                   type="textarea"
                   :rows="2"
-                  placeholder='请求头（JSON），可选，如 {"Content-Type": "application/json"}'
+                  placeholder="请求头（JSON），可选，如 {&quot;Content-Type&quot;: &quot;application/json&quot;}"
                 />
               </el-col>
               <el-col :span="24">
@@ -517,7 +517,7 @@
                   v-model="step.bodyText"
                   type="textarea"
                   :rows="3"
-                  placeholder='请求体（JSON），可选，支持 {{captured.key}} 变量，如 {"token": "{{captured.token}}"}'
+                  placeholder="请求体（JSON），可选，支持 {{captured.key}} 变量，如 {&quot;token&quot;: &quot;{{captured.token}}&quot;}"
                 />
               </el-col>
             </el-row>