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。

server/src/app/services/reimbursement.py

@@ -4,6 +4,7 @@ from app.core.logging import get_logger
 from app.models.reimbursement import ReimbursementRequest
 from app.repositories.reimbursement import ReimbursementRepository
 from app.schemas.reimbursement import ReimbursementCreate
+from app.services.pagination import PageResult
 
 logger = get_logger("app.services.reimbursement")
 
@@ -17,6 +18,22 @@ class ReimbursementService:
         logger.info("Listed reimbursements (count=%d)", len(items))
         return items
 
+    def list_reimbursements_page(
+        self,
+        *,
+        page: int | None,
+        page_size: int | None,
+    ) -> PageResult[ReimbursementRequest]:
+        result = self.repository.list_page(page=page, page_size=page_size)
+        logger.info(
+            "Listed reimbursements page (count=%d, total=%d, page=%d, page_size=%d)",
+            len(result.items),
+            result.total,
+            result.page,
+            result.page_size,
+        )
+        return result
+
     def get_reimbursement(self, request_id: str) -> ReimbursementRequest | None:
         request = self.repository.get(request_id)
         if request: