refactor: 前端全面替换 any 为 unknown 并统一错误处理，后端用量记录补写请求头/体

- 前端 API 层、stores、conversation 解析器、组件全面替换 any 为 unknown/具体类型
- 错误处理统一使用 parseApiError/getErrorStatus 替代 err.response?.data?.detail 模式
- 后端 handler/TaskService/UsageLifecycle/StreamTracker 链路传递 request_headers/request_body
- streaming/pending 状态更新时可补写客户端和提供商的请求头及请求体
- 新增 TaskService 和 UsageService 相关测试

frontend/src/views/shared/Usage.vue

@@ -291,7 +291,7 @@ async function pollActiveRequests() {
       if (shouldApply && record.status !== update.status) {
         record.status = update.status
       }
-      if (shouldApply && (update.status === 'completed' || update.status === 'failed')) {
+      if (shouldApply && ['completed', 'failed', 'cancelled'].includes(update.status)) {
         shouldRefresh = true
       }