feat: 添加完整的前端管理系统 (VbenAdmin)

- 添加基于 VbenAdmin + Vue3 + Element Plus 的前端管理系统
- 包含完整的 UI 组件库和工具链
- 支持多应用架构 (web-ele, backend-mock, playground)
- 包含完整的开发规范和配置
- 修复 admin 目录的子模块问题，确保正确提交

admin/packages/locales/src/typing.ts

@@ -0,0 +1,25 @@
+export type SupportedLanguagesType = 'en-US' | 'zh-CN';
+
+export type ImportLocaleFn = () => Promise<{ default: Record<string, string> }>;
+
+export type LoadMessageFn = (
+  lang: SupportedLanguagesType,
+) => Promise<Record<string, string> | undefined>;
+
+export interface LocaleSetupOptions {
+  /**
+   * Default language
+   * @default zh-CN
+   */
+  defaultLocale?: SupportedLanguagesType;
+  /**
+   * Load message function
+   * @param lang
+   * @returns
+   */
+  loadMessages?: LoadMessageFn;
+  /**
+   * Whether to warn when the key is not found
+   */
+  missingWarn?: boolean;
+}