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/Dashboard.vue

@@ -773,10 +773,12 @@
         {{ formatFullDate(selectedAnnouncement.created_at) }}
       </div>
 
+      <!-- eslint-disable vue/no-v-html -->
       <div
         class="prose prose-sm dark:prose-invert max-w-none"
         v-html="renderMarkdown(selectedAnnouncement.content)"
       />
+      <!-- eslint-enable vue/no-v-html -->
     </div>
 
     <template #footer>
@@ -998,7 +1000,7 @@ const loadingAnnouncements = ref(false)
 const selectedAnnouncement = ref<Announcement | null>(null)
 const detailDialogOpen = ref(false)
 
-const iconMap: Record<string, any> = {
+const iconMap: Record<string, unknown> = {
   Users, Activity, TrendingUp, DollarSign, Key, Hash, Database
 }