feat: 调优创建支持 SFT 自动合并权重

FineTuneTask 类型新增 auto_merge 字段，SFT 训练表单新增自动合并权重开关并在创建/启动时随参提交，回归脚本补充 auto_merge 与模型对话框断言。

frontend/src/views/fine-tune/FineTuneCreateView.vue

@@ -34,6 +34,7 @@ const form = reactive({
   template: 'qwen',
   train_method: 'lora' as 'lora' | 'full',
   train_dataset_id: '' as string | number,
+  auto_merge: false,
   // 训练参数
   batch_size: 1,
   learning_rate: 0.0001,
@@ -216,6 +217,7 @@ async function handleSubmit() {
         train_method: form.train_method,
         gpus: selectedGpus.value,
         train_dataset_id: form.train_dataset_id,
+        auto_merge: form.train_type === 'SFT' && form.auto_merge,
         output_model_name: form.name,
         batch_size: form.batch_size,
         learning_rate: form.learning_rate,
@@ -244,6 +246,7 @@ async function handleSubmit() {
           train_type: form.train_type,
           train_method: form.train_method,
           train_dataset_id: form.train_dataset_id,
+          auto_merge: form.train_type === 'SFT' && form.auto_merge,
           output_model_name: form.name,
           gpus: selectedGpus.value,
           batch_size: form.batch_size,
@@ -424,6 +427,16 @@ onMounted(() => {
           </el-select>
         </el-form-item>
 
+        <template v-if="form.train_type === 'SFT'">
+          <el-divider content-position="left">合并模型</el-divider>
+          <el-form-item label="自动合并权重并保存">
+            <el-select v-model="form.auto_merge" style="width: 420px;">
+              <el-option label="否" :value="false" />
+              <el-option label="是" :value="true" />
+            </el-select>
+          </el-form-item>
+        </template>
+
         <!-- 训练命令预览 -->
         <el-divider content-position="left">训练命令预览</el-divider>
         <div class="command-preview-wrapper">