style: 全局 UI 主题皮肤重构与样式模块化

引入 Element Plus 主题定制和主题皮肤 composable，将全局
样式拆分为组件级独立 CSS 文件（侧边栏、顶栏、工作台等），
统一色彩变量和间距规范，重构所有视图和组件样式以适配新
主题系统，优化图表和知识图谱组件视觉表现，提取审计和差
旅报销相关子组件。

web/src/main.js

@@ -1,26 +1,22 @@
 import { createApp } from 'vue'
 import { MotionPlugin } from '@vueuse/motion'
-import PrimeVue from 'primevue/config'
-import Aura from '@primevue/themes/aura'
+import ElementPlus from 'element-plus'
+import zhCn from 'element-plus/es/locale/lang/zh-cn'
+import 'element-plus/dist/index.css'
 import 'primeicons/primeicons.css'
 import App from './App.vue'
 import router from './router/index.js'
+import { installThemeSkin } from './composables/useThemeSkin.js'
 import { installSessionNavigation } from './composables/useSystemState.js'
+import './assets/styles/element-plus-theme.css'
 
 const app = createApp(App)
 
+installThemeSkin()
 installSessionNavigation(router)
 
 app.use(MotionPlugin)
 app.use(router)
-app.use(PrimeVue, {
-  theme: {
-    preset: Aura,
-    options: {
-      darkModeSelector: '.dark',
-      cssLayer: false
-    }
-  }
-})
+app.use(ElementPlus, { locale: zhCn })
 
 app.mount('#app')