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/playground/src/views/dashboard/analytics/analytics-visits-source.vue

@@ -0,0 +1,65 @@
+<script lang="ts" setup>
+import type { EchartsUIType } from '@vben/plugins/echarts';
+
+import { onMounted, ref } from 'vue';
+
+import { EchartsUI, useEcharts } from '@vben/plugins/echarts';
+
+const chartRef = ref<EchartsUIType>();
+const { renderEcharts } = useEcharts(chartRef);
+
+onMounted(() => {
+  renderEcharts({
+    legend: {
+      bottom: '2%',
+      left: 'center',
+    },
+    series: [
+      {
+        animationDelay() {
+          return Math.random() * 100;
+        },
+        animationEasing: 'exponentialInOut',
+        animationType: 'scale',
+        avoidLabelOverlap: false,
+        color: ['#5ab1ef', '#b6a2de', '#67e0e3', '#2ec7c9'],
+        data: [
+          { name: '搜索引擎', value: 1048 },
+          { name: '直接访问', value: 735 },
+          { name: '邮件营销', value: 580 },
+          { name: '联盟广告', value: 484 },
+        ],
+        emphasis: {
+          label: {
+            fontSize: '12',
+            fontWeight: 'bold',
+            show: true,
+          },
+        },
+        itemStyle: {
+          // borderColor: '#fff',
+          borderRadius: 10,
+          borderWidth: 2,
+        },
+        label: {
+          position: 'center',
+          show: false,
+        },
+        labelLine: {
+          show: false,
+        },
+        name: '访问来源',
+        radius: ['40%', '65%'],
+        type: 'pie',
+      },
+    ],
+    tooltip: {
+      trigger: 'item',
+    },
+  });
+});
+</script>
+
+<template>
+  <EchartsUI ref="chartRef" />
+</template>