ux: 部门字段统一改为下拉选择（组织架构部门树）

将以下页面的部门输入框从 Input 改为 Select 下拉选择，
数据源为组织架构部门树（带层级缩进）：

1. roster/modals.tsx - RehireModal 重新入职弹窗
2. roster/modals.tsx - AddEmployeeModal 添加员工弹窗
3. roster/BasicInfo.tsx - 编辑员工基本信息
4. Contracts.tsx - 合同管理新增员工弹窗

下拉选项从 /departments 接口获取，按树形结构展示，
提交时传部门名称字符串（保持后端兼容）。

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

frontend/src/pages/roster/BasicInfo.tsx

@@ -5,6 +5,7 @@ import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query"
 import { attachmentApi, employeeApi, socialInsuranceApi } from '../../lib/api-services'
 import { useConfirm } from '../../hooks/useConfirm'
 import { copyToClipboard } from '../../lib/clipboard'
+import api from '../../lib/api'
 import Card from "../../components/ui/Card"
 import Button from "../../components/ui/Button"
 import { Input, Label, Select } from "../../components/ui/Input"
@@ -58,6 +59,21 @@ export default function BasicInfo({ profile, employeeId, attachments }: { profil
     return `${(bytes / 1024 / 1024).toFixed(1)}MB`
   }
 
+  // 拉取组织架构部门列表，用于部门下拉选择
+  const { data: departments = [] } = useQuery({
+    queryKey: ['departments'],
+    queryFn: () => api.get('/departments').then(r => r.data),
+  })
+  // 构建部门树形下拉选项（带层级缩进）
+  const deptOptions: { id: string; label: string; level: number }[] = []
+  const buildDeptOptions = (items: any[], parentId: string | null, level: number) => {
+    items.filter(d => d.parentId === parentId).sort((a, b) => a.sortOrder - b.sortOrder).forEach(d => {
+      deptOptions.push({ id: d.id, label: d.name, level })
+      buildDeptOptions(items, d.id, level + 1)
+    })
+  }
+  buildDeptOptions(departments, null, 0)
+
   const [form, setForm] = useState({
     department: profile.department || '',
     position: profile.position || '',
@@ -346,7 +362,7 @@ export default function BasicInfo({ profile, employeeId, attachments }: { profil
         <div className="grid md:grid-cols-2 gap-3">
           <div><Label>姓名（不可编辑）</Label><Input value={profile.name} disabled /></div>
           <div><Label>证件号码（不可编辑）</Label><Input value={profile.idCardNumber || ''} disabled /></div>
-          <div><Label>部门</Label><Input value={form.department} onChange={(e) => setForm({ ...form, department: e.target.value })} /></div>
+          <div><Label>部门</Label><Select value={form.department} onChange={(e) => setForm({ ...form, department: e.target.value })}><option value="">请选择部门</option>{deptOptions.map(d => <option key={d.id} value={d.label}>{'　'.repeat(d.level)}{d.label}</option>)}</Select></div>
           <div><Label>性别</Label><Select value={form.gender} onChange={(e) => setForm({ ...form, gender: e.target.value as '男' | '女' })}><option value="男">男</option><option value="女">女</option></Select></div>
           {form.gender === '女' && (
             <div><Label>女性岗位类型</Label><Select value={form.femaleWorkerType} onChange={(e) => setForm({ ...form, femaleWorkerType: e.target.value as '' | 'CADRE' | 'WORKER' })}><option value="">未选择</option><option value="CADRE">干部/管理岗</option><option value="WORKER">工人/操作岗</option></Select></div>