feat: 前端离线部署适配与在线模型测试延迟展示

- 移除 index.html 中 Google Fonts 外链，适配离线部署环境
- 侧边栏用户头像改为显示姓名首字母，去掉 picsum 占位图外链
- 在线模型测试补充 latency_ms 延迟字段展示
- api_key 为空时传空字符串避免校验报错

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

frontend/src/views/model/ModelCreateView.vue

@@ -38,7 +38,13 @@ const form = reactive<ModelForm>({
 
 // 在线模型测试
 const testLoading = ref(false)
-const testResult = ref<{ success: boolean; error?: string; model?: string; usage?: object } | null>(null)
+const testResult = ref<{
+  success: boolean
+  error?: string
+  model?: string
+  usage?: object
+  latency_ms?: number
+} | null>(null)
 
 const rules: FormRules = {
   name: [
@@ -149,7 +155,7 @@ async function handleTestOnline() {
     const start = Date.now()
     const res = await testOnlineModel({
       api_url: form.api_url,
-      api_key: form.api_key,
+      api_key: form.api_key || '',
       online_model_name: form.online_model_name,
     })
     const data = res as any