feat: 新增 cancelled 状态区分客户端主动断开连接

- 新增 cancelled 请求状态，与系统失败 (failed) 区分
- 客户端主动断开连接 (HTTP 499) 不计入失败率统计
- 前后端同步更新状态枚举、UI 样式和统计逻辑

frontend/src/mocks/handler.ts

@@ -1219,8 +1219,8 @@ function generateMockEndpointsForProvider(providerId: string) {
       provider_name: provider.name,
       api_format: format,
       base_url: format.includes('CLAUDE') ? 'https://api.anthropic.com' :
-                format.includes('OPENAI') ? 'https://api.openai.com' :
-                'https://generativelanguage.googleapis.com',
+        format.includes('OPENAI') ? 'https://api.openai.com' :
+          'https://generativelanguage.googleapis.com',
       max_retries: 2,
       is_active: healthDetail?.is_active ?? true,
       total_keys: Math.ceil(Math.random() * 3) + 1,