feat: 模型推理异步加载与对话链路修复，同步基线

模型推理全异步化改造：
- 计算节点 InferenceSession 改为后台线程异步加载模型，load 立即返回，
  加载期间事件循环保持响应（/inference/status 与 /health 不阻塞）
- 后端模型加载改为异步派发 + 轮询对账器（reconcile_inference_loads），
  任务状态由 starting 自动推进到 ready/error，解决多节点启动超时
  （timeout of 120000ms exceeded）
- 推理删除/卸载改为任务感知 + 短超时，删除先删记录再 best-effort 卸载，
  不再被不可达节点阻塞；同节点新模型替换旧任务标记失效
- 流式对话透传 task_id/node_id 路由到真正加载模型的算力节点，
  useStreamChat 解析 SSE 错误帧以干净文案展示
- 对话历史按任务 id 本地持久化，退出重进可恢复；移除页脚提示文本
- 新增后端推理异步加载与计算节点异步状态机单元测试

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/views/model/MergeWeightsView.vue

@@ -18,9 +18,12 @@ const trainedModels = ref<TrainedModel[]>([])
 const currentModel = computed(() => trainedModels.value.find((m) => m.name === modelName.value))
 
 const form = reactive({
+  trained_model_id: '',
   model_name: modelName.value,
   train_method: method.value,
   base_model_path: '',
+  adapter_path: '',
+  compute_node_id: '',
 })
 
 async function loadModel() {
@@ -28,23 +31,30 @@ async function loadModel() {
     const res = await getTrainedModels()
     trainedModels.value = res?.models || []
     const target = trainedModels.value.find((m) => m.name === modelName.value)
+    form.trained_model_id = target?.id == null ? '' : String(target.id)
     form.base_model_path = target?.base_model_path || ''
+    form.adapter_path = target?.artifact_dir || target?.adapter_path || target?.merged_path || ''
+    form.compute_node_id = target?.compute_node_id || ''
   } catch {
     // ignore
   }
 }
 
 async function handleMerge() {
-  if (!form.model_name || !form.base_model_path) {
+  if (!form.model_name || !form.base_model_path || !form.adapter_path) {
     ElMessage.warning('缺少模型信息')
     return
   }
   merging.value = true
   try {
     await mergeModel({
+      trained_model_id: form.trained_model_id || form.model_name,
       model_name: form.model_name,
       train_method: form.train_method,
       base_model_path: form.base_model_path,
+      adapter_path: form.adapter_path,
+      compute_node_id: form.compute_node_id,
+      output_model_name: `${form.model_name}-merged`,
     })
     ElMessage.success('合并成功')
     router.push('/model-manage')
@@ -82,6 +92,9 @@ onMounted(loadModel)
       <el-form-item label="基座模型路径">
         <el-input v-model="form.base_model_path" placeholder="基座模型路径" />
       </el-form-item>
+      <el-form-item label="Adapter 路径">
+        <el-input v-model="form.adapter_path" placeholder="LoRA Adapter 权重目录" />
+      </el-form-item>
 
       <el-form-item>
         <el-button type="primary" :loading="merging" @click="handleMerge">