refactor(KnowledgeItemEditor): 重构知识项编辑器组件结构

- 提取创建模式判断逻辑为独立变量 isCreateMode
- 使用条件渲染替代原有的 data?.id 判断
- 将表单字段按照创建和编辑模式进行分组重构
- 优化文件上传和替换功能的显示逻辑
- 改进代码可读性和维护性

frontend/src/pages/KnowledgeManagement/components/KnowledgeItemEditor.tsx

@@ -51,7 +51,8 @@ export default function KnowledgeItemEditor({
   const isFileItem =
     data?.contentType === KnowledgeContentType.FILE ||
     data?.sourceType === KnowledgeSourceType.FILE_UPLOAD;
-  const contentTypeLabel = !data?.id
+  const isCreateMode = !data?.id;
+  const contentTypeLabel = isCreateMode
     ? "文件"
     : data?.contentType === KnowledgeContentType.MARKDOWN
       ? "Markdown"
@@ -294,22 +295,7 @@ export default function KnowledgeItemEditor({
       okButtonProps={{ disabled: readOnly }}
     >
       <Form form={form} layout="vertical" disabled={readOnly}>
-        <div className="grid grid-cols-2 gap-4">
-          <Form.Item
-            label="标题"
-            name="title"
-            rules={[{ required: !isMultiFile, message: "请输入标题" }]}
-          >
-            <Input
-              placeholder={isMultiFile ? "多文件将按文件名自动生成" : "请输入标题"}
-              disabled={readOnly || (!data?.id && isMultiFile)}
-            />
-          </Form.Item>
-          <Form.Item label="状态" name="status">
-            <Select options={knowledgeStatusOptions} />
-          </Form.Item>
-        </div>
-        {!data?.id && (
+        {isCreateMode && (
           <Form.Item label="上传文件" required>
             <Upload
               beforeUpload={handleFileBeforeUpload}
@@ -326,6 +312,23 @@ export default function KnowledgeItemEditor({
             </div>
           </Form.Item>
         )}
+        {!isCreateMode && (
+          <>
+            <div className="grid grid-cols-2 gap-4">
+              <Form.Item
+                label="标题"
+                name="title"
+                rules={[{ required: !isMultiFile, message: "请输入标题" }]}
+              >
+                <Input
+                  placeholder={isMultiFile ? "多文件将按文件名自动生成" : "请输入标题"}
+                  disabled={readOnly || (!data?.id && isMultiFile)}
+                />
+              </Form.Item>
+              <Form.Item label="状态" name="status">
+                <Select options={knowledgeStatusOptions} />
+              </Form.Item>
+            </div>
             {data?.id && isFileItem && (
               <Form.Item label="文件">
                 <div className="flex items-center gap-2">
@@ -397,6 +400,8 @@ export default function KnowledgeItemEditor({
                 <div>来源文件：{data.sourceFileId || "-"}</div>
               </div>
             )}
+          </>
+        )}
       </Form>
     </Modal>
   );