feat(knowledge): 移除知识库管理中的敏感级别功能

- 注释掉创建知识集表单中的敏感级别选择字段
- 移除知识集详情页面中的敏感级别显示项
- 注释掉相关的敏感级别选项配置常量
- 更新表单布局以保持一致的两列网格结构

frontend/src/pages/KnowledgeManagement/Detail/KnowledgeSetDetail.tsx

@@ -991,7 +991,7 @@ const KnowledgeSetDetail = () => {
           <Descriptions.Item label="领域">{knowledgeSet?.domain || "-"}</Descriptions.Item>
           <Descriptions.Item label="业务线">{knowledgeSet?.businessLine || "-"}</Descriptions.Item>
           <Descriptions.Item label="负责人">{knowledgeSet?.owner || "-"}</Descriptions.Item>
-          <Descriptions.Item label="敏感级别">{knowledgeSet?.sensitivity || "-"}</Descriptions.Item>
+          {/* <Descriptions.Item label="敏感级别">{knowledgeSet?.sensitivity || "-"}</Descriptions.Item> */}
           <Descriptions.Item label="有效期">
             {knowledgeSet?.validFrom || "-"} ~ {knowledgeSet?.validTo || "-"}
           </Descriptions.Item>