feat: 后台一键刷新飞书缓存

- feishu_service.py: FeishuKnowledgeService 新增 clear_cache() 方法
- admin_settings.py: 新增 POST /admin/feishu/cache/clear API
- api.ts: 前端封装 clearFeishuCache API
- App.vue: Agent管理页面新增'刷新飞书缓存'按钮

管理员更新飞书文档后，点击按钮即可清空服务端内存缓存，
客户端下次提问时会重新读取最新内容。

ai_knowledge_base_v2/apps/admin-web/src/services/api.ts

@@ -135,4 +135,6 @@ export const api = {
   aiLogs: (query: { sessionId?: number; userId?: number; status?: string } = {}) =>
     request<AiLogRecord[]>(`/admin/ai-log/list${queryString(query)}`),
   operationLogs: () => request<Record<string, unknown>[]>("/admin/log/list"),
+  clearFeishuCache: () =>
+    request<{ cleared: number; message: string }>("/admin/feishu/cache/clear", { method: "POST", body: "{}" }),
 };