refactor: 前端构建按需化与 Mock 懒加载

移除全量 Element Plus 与全局 VChart 注册，改为按需引入样式与组件内局部图表；Mock 适配器改为按 VITE_ENABLE_MOCK 环境变量懒加载，生产默认不拦截请求；ECharts 精简为看板所需图表，各视图与 stores 同步适配。

frontend/src/views/dashboard/DashboardView.vue

@@ -1,6 +1,8 @@
 <script setup lang="ts">
 import { computed, ref } from 'vue'
 import { useRouter } from 'vue-router'
+import VChart from 'vue-echarts'
+import '@/plugins/echarts'
 import type { EChartsOption } from 'echarts'
 
 type ServiceState = 'normal' | 'busy' | 'error'
@@ -253,7 +255,7 @@ const loginDurationStats: LoginDurationStat[] = [
 
 const loginDurationChartOption = computed<EChartsOption>(() => ({
   animationDuration: 500,
-  grid: { top: 8, right: 60, bottom: 6, left: 8, containLabel: true },
+  grid: { top: 8, right: 12, bottom: 6, left: 8, containLabel: true },
   tooltip: {
     trigger: 'axis',
     axisPointer: { type: 'shadow' },
@@ -284,7 +286,7 @@ const loginDurationChartOption = computed<EChartsOption>(() => ({
       barMaxWidth: 18,
       barCategoryGap: '34%',
       itemStyle: { color: '#4f46e5', borderRadius: [0, 4, 4, 0] },
-      label: { show: true, position: 'right', distance: 6, color: '#64748b', fontSize: 11, formatter: '{c} 小时' },
+      label: { show: true, position: 'insideRight', distance: 6, color: '#ffffff', fontSize: 11, formatter: '{c} 小时' },
     },
   ],
 }))