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/expense_claims.py

@@ -48,6 +48,7 @@ from app.services.expense_claim_document_parsing import ExpenseClaimDocumentPars
 from app.services.expense_claim_draft_flow import ExpenseClaimDraftFlowMixin
 from app.services.expense_claim_draft_persistence import ExpenseClaimDraftPersistenceMixin
 from app.services.expense_claim_errors import ExpenseClaimSubmissionBlockedError
+from app.services.expense_claim_pagination import ExpenseClaimPaginationMixin
 from app.services.expense_claim_ontology_resolvers import ExpenseClaimOntologyResolverMixin
 from app.services.expense_claim_read_model import ExpenseClaimReadModelMixin
 from app.services.expense_claim_review_preview import ExpenseClaimReviewPreviewMixin
@@ -128,6 +129,7 @@ from app.services.ocr import OcrService
 
 
 class ExpenseClaimService(
+    ExpenseClaimPaginationMixin,
     ExpenseClaimApprovalFlowMixin,
     ExpenseClaimApplicationHandoffMixin,
     ExpenseClaimBudgetFlowMixin,