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/pagination.py

@@ -0,0 +1,95 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+from dataclasses import dataclass
+from math import ceil
+from typing import Any, Generic, TypeVar
+
+from sqlalchemy import func, select
+from sqlalchemy.orm import Session
+from sqlalchemy.sql import Select
+
+T = TypeVar("T")
+U = TypeVar("U")
+
+DEFAULT_PAGE = 1
+DEFAULT_PAGE_SIZE = 20
+MAX_PAGE_SIZE = 100
+
+
+@dataclass(frozen=True)
+class PageParams:
+    page: int
+    page_size: int
+
+    @property
+    def offset(self) -> int:
+        return (self.page - 1) * self.page_size
+
+
+@dataclass(frozen=True)
+class PageResult(Generic[T]):
+    items: list[T]
+    total: int
+    page: int
+    page_size: int
+
+    @property
+    def total_pages(self) -> int:
+        if self.total <= 0:
+            return 0
+        return ceil(self.total / self.page_size)
+
+    @property
+    def has_next(self) -> bool:
+        return self.page < self.total_pages
+
+    @property
+    def has_previous(self) -> bool:
+        return self.page > 1 and self.total_pages > 0
+
+    def map(self, mapper: Callable[[T], U]) -> PageResult[U]:
+        return PageResult(
+            items=[mapper(item) for item in self.items],
+            total=self.total,
+            page=self.page,
+            page_size=self.page_size,
+        )
+
+
+def normalize_page_params(
+    page: int | None,
+    page_size: int | None,
+    *,
+    max_page_size: int = MAX_PAGE_SIZE,
+) -> PageParams:
+    normalized_page = max(DEFAULT_PAGE, int(page or DEFAULT_PAGE))
+    normalized_page_size = max(1, int(page_size or DEFAULT_PAGE_SIZE))
+    normalized_page_size = min(normalized_page_size, max_page_size)
+    return PageParams(page=normalized_page, page_size=normalized_page_size)
+
+
+def paginate_select(
+    db: Session,
+    stmt: Select[Any],
+    *,
+    page: int | None,
+    page_size: int | None,
+    max_page_size: int = MAX_PAGE_SIZE,
+    unique: bool = False,
+) -> PageResult[Any]:
+    params = normalize_page_params(page, page_size, max_page_size=max_page_size)
+    count_stmt = select(func.count()).select_from(stmt.order_by(None).subquery())
+    total = int(db.scalar(count_stmt) or 0)
+
+    page_stmt = stmt.limit(params.page_size).offset(params.offset)
+    scalars = db.execute(page_stmt).scalars()
+    if unique:
+        scalars = scalars.unique()
+
+    return PageResult(
+        items=list(scalars.all()),
+        total=total,
+        page=params.page,
+        page_size=params.page_size,
+    )