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/App.vue

@@ -912,6 +912,15 @@ function clearAgentPreview() {
   ];
 }
 
+async function clearFeishuCache() {
+  try {
+    const result = await api.clearFeishuCache();
+    ElMessage.success(result.message || `已清空 ${result.cleared} 条缓存`);
+  } catch (e: any) {
+    ElMessage.error(e.message || "刷新缓存失败");
+  }
+}
+
 async function searchChats() {
   chats.value = await api.chats(buildChatQuery());
 }
@@ -1163,6 +1172,7 @@ function buildChatQuery() {
                 <div class="actions">
                   <el-button type="primary" @click="savePrompt">保存 Agent 提示词</el-button>
                   <el-button @click="clearAgentPreview">清空预览</el-button>
+                  <el-button type="warning" @click="clearFeishuCache">刷新飞书缓存</el-button>
                 </div>
               </el-form>
             </div>