feat(布局): 添加应用配置常量并更新主布局标题显示

将网站标题配置提取到单独的配置文件
根据折叠状态动态调整标题字体大小

frontend/src/layouts/MainLayout.tsx

@@ -6,6 +6,7 @@ import { clearToken, getUser as getUserLocal, setUser as setUserLocal } from '..
 import api from '../utils/axios'
 import './layout.css'
 import { PermissionProvider } from '../utils/permission'
+import { APP_CONFIG } from '../utils/config'
 const { Header, Sider, Content } = Layout
 
 interface MenuItemResp { id: number; parent_id?: number | null; name: string; path?: string | null; component?: string | null; type: number; icon?: string | null; order_no: number; visible: boolean; status: number; perms?: string | null; keep_alive?: boolean }
@@ -457,11 +458,20 @@ export default function MainLayout() {
       style={{ background: colorBgContainer }}
       >
         <div
-          style={{ height: 64, display: 'flex', alignItems: 'center', justifyContent: 'center', fontWeight: 600, cursor: 'pointer', userSelect: 'none' }}
+          style={{ 
+            height: 64, 
+            display: 'flex', 
+            alignItems: 'center', 
+            justifyContent: 'center', 
+            fontWeight: 600, 
+            fontSize: leftCollapsed ? '16px' : '18px',
+            cursor: 'pointer', 
+            userSelect: 'none' 
+          }}
           onClick={() => setLeftCollapsed(c => !c)}
           title={leftCollapsed ? '展开菜单' : '收起菜单'}
         >
-          {leftCollapsed ? '道友' : '道友管理系统'}
+          {leftCollapsed ? APP_CONFIG.SITE_NAME_SHORT : APP_CONFIG.SITE_NAME}
         </div>
          <Menu
            mode="inline"

frontend/src/utils/config.ts

@@ -0,0 +1,11 @@
+// 前端系统配置常量
+export const APP_CONFIG = {
+  // 网站标题配置
+  SITE_NAME: '道友管理系统',
+  SITE_NAME_SHORT: '道友',
+  
+  // 其他系统配置可以在这里添加
+  // 如: API_VERSION: 'v1', DEFAULT_PAGE_SIZE: 10 等
+} as const
+
+export default APP_CONFIG