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/tests/test_agent_asset_service.py

@@ -156,6 +156,22 @@ def test_agent_asset_service_seeds_all_foundation_asset_types() -> None:
         assert len(service.list_assets(asset_type=AgentAssetType.TASK.value)) >= 3
 
 
+def test_agent_asset_service_supports_backend_pagination() -> None:
+    with build_session() as db:
+        service = AgentAssetService(db)
+
+        page = service.list_assets_page(
+            asset_type=AgentAssetType.RULE.value,
+            page=1,
+            page_size=2,
+        )
+
+        assert len(page.items) <= 2
+        assert page.total >= len(page.items)
+        assert page.page == 1
+        assert page.page_size == 2
+
+
 def test_finance_rules_use_risk_rule_scenario_categories() -> None:
     with build_session() as db:
         service = AgentAssetService(db)