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/vite.config.ts

@@ -10,10 +10,10 @@ export default defineConfig({
   plugins: [
     vue(),
     AutoImport({
-      resolvers: [ElementPlusResolver({ importStyle: false })],
+      resolvers: [ElementPlusResolver({ importStyle: 'css' })],
     }),
     Components({
-      resolvers: [ElementPlusResolver({ importStyle: false })],
+      resolvers: [ElementPlusResolver({ importStyle: 'css' })],
     }),
   ],
   resolve: {