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/views/RequestsView.vue

@@ -135,14 +135,13 @@
           <button v-for="p in totalPages" :key="p" class="page-number" :class="{ active: currentPage === p }" type="button" :aria-current="currentPage === p ? 'page' : undefined" @click="currentPage = p">{{ p }}</button>
           <button class="page-nav" type="button" :disabled="currentPage === totalPages" aria-label="下一页" @click="currentPage++"><i class="mdi mdi-chevron-right"></i></button>
         </div>
-        <div class="page-size-wrap">
-          <button class="page-size" type="button" @click="pageSizeOpen = !pageSizeOpen">
-            {{ pageSize }} 条/页 <i class="mdi mdi-chevron-down"></i>
-          </button>
-          <div v-if="pageSizeOpen" class="page-size-dropdown" role="listbox">
-            <button v-for="size in pageSizes" :key="size" type="button" role="option" :aria-selected="pageSize === size" :class="{ active: pageSize === size }" @click="changePageSize(size)">{{ size }} 条/页</button>
-          </div>
-        </div>
+        <EnterpriseSelect
+          v-model="pageSize"
+          class="page-size-select"
+          :options="pageSizeOptions"
+          size="small"
+          @change="changePageSize"
+        />
       </footer>
     </article>
   </section>