feat(admin): 添加后台显示设置功能

- 新增后台显示设置页面，允许自定义布局标题
- 在布局组件中动态显示自定义标题
- 在后端添加对应的 API 端点用于获取和保存显示配置
- 移除无用的 Demo.vue 组件文件

cwd-admin/src/api/admin.ts

@@ -128,6 +128,10 @@ export type FeatureSettingsResponse = {
 	enableArticleLike: boolean;
 };
 
+export type AdminDisplaySettingsResponse = {
+	layoutTitle: string | null;
+};
+
 export async function loginAdmin(name: string, password: string): Promise<string> {
 	const res = await post<AdminLoginResponse>('/admin/login', { name, password });
 	const key = res.data.key;
@@ -327,6 +331,16 @@ export function saveFeatureSettings(data: { enableCommentLike?: boolean; enableA
 	return put<{ message: string }>('/admin/settings/features', data);
 }
 
+export function fetchAdminDisplaySettings(): Promise<AdminDisplaySettingsResponse> {
+	return get<AdminDisplaySettingsResponse>('/admin/settings/admin-display');
+}
+
+export function saveAdminDisplaySettings(data: {
+	layoutTitle?: string;
+}): Promise<{ message: string }> {
+	return put<{ message: string }>('/admin/settings/admin-display', data);
+}
+
 export type TelegramSettingsResponse = {
 	botToken: string | null;
 	chatId: string | null;