chore: 初始化前端仓库并迁移 admin-ui

- 创建 rui-frontend 前端仓库
- 迁移 admin-ui 管理后台
- 创建 cashier-mobile 和 customer-mobile 占位项目
- 配置 pnpm workspace

admin-ui/src/App.vue

@@ -0,0 +1,69 @@
+<script setup lang="ts">
+import { computed, onMounted } from 'vue'
+import { useAppStore } from '@/stores/app'
+import zhCn from 'element-plus/es/locale/lang/zh-cn'
+import en from 'element-plus/es/locale/lang/en'
+import systemConfig from 'virtual:system-config'
+
+const app = useAppStore()
+const locale = computed(() => app.lang === 'zh-CN' ? zhCn : en)
+
+onMounted(() => {
+  // 设置页面标题
+  document.title = systemConfig.theme.title
+  
+  // 设置主题色
+  const el = document.documentElement
+  el.style.setProperty('--el-color-primary', systemConfig.theme.primaryColor)
+})
+</script>
+
+<template>
+  <el-config-provider :locale="locale">
+    <router-view />
+    <!-- 全屏退出角标 -->
+    <div v-if="app.pageFullscreen" class="fs-exit" @click="app.togglePageFullscreen()">
+      <el-icon :size="18"><Close /></el-icon>
+    </div>
+  </el-config-provider>
+</template>
+
+<style>
+:root { --el-bg-color-page: #f5f6fa; }
+html.dark { --el-bg-color-page: #111; color-scheme: dark; }
+html.dark body { background: #111; color: #e5e7eb; }
+
+.fullscreen-main {
+  position: fixed !important; inset: 0 !important; z-index: 100 !important;
+  background: #f5f6fa !important; padding: 20px !important; overflow: auto !important;
+}
+html.dark .fullscreen-main { background: #111 !important; }
+
+.fs-exit {
+  position: fixed; top: 16px; right: 16px; z-index: 200;
+  width: 36px; height: 36px; border-radius: 50%;
+  background: rgba(0,0,0,0.4); color: #fff;
+  display: flex; align-items: center; justify-content: center;
+  cursor: pointer; transition: all 0.2s;
+}
+.fs-exit:hover { background: rgba(0,0,0,0.6); }
+
+/* ======================== rui-dialog 全局样式规则 ======================== */
+/**
+ * 所有使用 el-dialog 的组件必须添加 class="rui-dialog"
+ * 规则说明：
+ * 1. 内容区域最大高度 60vh，超出滚动
+ * 2. 底部 footer 固定不参与滚动
+ * 3. 用法：<el-dialog class="rui-dialog" ...>
+ */
+.rui-dialog .el-dialog__body {
+  max-height: 60vh;
+  overflow-y: auto;
+  padding: 20px;
+}
+.rui-dialog .el-dialog__footer {
+  border-top: 1px solid var(--el-border-color-lighter);
+  padding: 12px 20px;
+  background: var(--el-bg-color);
+}
+</style>