feat: 统一后端分页查询与前端服务层适配

后端新增通用分页模块，为报销单、员工、预算、agent 资产等
端点统一接入分页参数和游标查询，优化 repository 层分页实
现，前端服务层适配分页响应结构，完善预算图表和全局样式，
优化侧边栏和企业选择器组件，引入 Element Plus 插件注册。

web/src/services/budgets.js

@@ -4,7 +4,7 @@ function buildQuery(params = {}) {
   const search = new URLSearchParams()
   Object.entries(params || {}).forEach(([key, value]) => {
     if (typeof value === 'undefined' || value === null || value === '') return
-    search.set(key, String(value))
+    search.set(key === 'pageSize' ? 'page_size' : key, String(value))
   })
   const query = search.toString()
   return query ? `?${query}` : ''
@@ -25,6 +25,7 @@ export function createBudgetAllocation(payload = {}) {
   })
 }
 
-export function fetchBudgetTransactions(allocationId) {
-  return apiRequest(`/budgets/allocations/${encodeURIComponent(String(allocationId || '').trim())}/transactions`)
+export function fetchBudgetTransactions(allocationId, params = {}) {
+  const encodedId = encodeURIComponent(String(allocationId || '').trim())
+  return apiRequest(`/budgets/allocations/${encodedId}/transactions${buildQuery(params)}`)
 }