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/utils/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "@vben/utils",
+  "version": "5.5.9",
+  "homepage": "https://github.com/vbenjs/vue-vben-admin",
+  "bugs": "https://github.com/vbenjs/vue-vben-admin/issues",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/vbenjs/vue-vben-admin.git",
+    "directory": "packages/utils"
+  },
+  "license": "MIT",
+  "type": "module",
+  "sideEffects": [
+    "**/*.css"
+  ],
+  "exports": {
+    ".": {
+      "types": "./src/index.ts",
+      "default": "./src/index.ts"
+    }
+  },
+  "dependencies": {
+    "@vben-core/shared": "workspace:*",
+    "@vben-core/typings": "workspace:*",
+    "vue-router": "catalog:"
+  }
+}