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/backend/app/api/admin_settings.py

@@ -302,6 +302,12 @@ def _build_agent_debug_prompt(prompt_content: str, question: str, chunks: list)
     return f"{prompt_content.strip()}\n\n{context}\n\n用户问题：{question.strip()}"
 
 
+@router.post("/feishu/cache/clear")
+def clear_feishu_cache(current_admin: Admin = Depends(get_current_admin)) -> dict:
+    count = FeishuKnowledgeService.clear_cache()
+    return api_success({"cleared": count, "message": f"已清空 {count} 条飞书缓存"})
+
+
 def _config_dict(config: SystemConfig) -> dict:
     return {
         "id": config.id,

ai_knowledge_base_v2/apps/backend/app/services/feishu_service.py

@@ -323,6 +323,13 @@ class FeishuKnowledgeService:
     _content_cache: dict[str, tuple[str, float]] = {}
     _CACHE_TTL = 300  # 缓存 5 分钟
 
+    @classmethod
+    def clear_cache(cls) -> int:
+        """清空所有飞书内容缓存，返回被清除的条目数"""
+        count = len(cls._content_cache)
+        cls._content_cache.clear()
+        return count
+
     @classmethod
     def retrieve(
         cls,