fix: HR系统优化批次1 - P0/P1问题修复

P0-3: 修复合同状态判断逻辑，有合同记录但signDate为null时不再误判未签
P0-5: 修复参保城市默认北京问题，导入和预览均改为null
P0-11: 添加全局ErrorBoundary防止白屏，三处布局均包裹
P1-2: 合同附件改为可选，允许先保存再补充上传
P1-7.2: 排班弹窗增加员工搜索（姓名/部门）
P1-8.2: 加班费导入支持Excel(xlsx/xls)格式，兼容中英文列名
P1-9: 社保/公积金基数月度办理支持逐人修改，后端返回recordId

frontend/src/pages/Attendance.tsx

@@ -468,6 +468,7 @@ function ScheduleTab() {
   const [showAssign, setShowAssign] = useState(false)
   const [selectedShiftId, setSelectedShiftId] = useState('')
   const [selectedEmployeeIds, setSelectedEmployeeIds] = useState<Set<string>>(new Set())
+  const [searchQuery, setSearchQuery] = useState('')
 
   const { data: shifts } = useQuery<any>({
     queryKey: ['shifts'],
@@ -602,8 +603,19 @@ function ScheduleTab() {
           </div>
           <div>
             <Label>选择员工（{selectedEmployeeIds.size} 人已选）</Label>
+            <input
+              type="text"
+              placeholder="搜索员工姓名或部门..."
+              value={searchQuery}
+              onChange={e => setSearchQuery(e.target.value)}
+              className="w-full px-3 py-2 mb-2 text-sm border rounded-lg focus:outline-none focus:ring-2 focus:ring-primary"
+            />
             <div className="max-h-60 overflow-y-auto border rounded-lg divide-y">
-              {employees.map((emp: any) => (
+              {employees.filter((emp: any) => {
+                if (!searchQuery.trim()) return true
+                const q = searchQuery.trim().toLowerCase()
+                return emp.name?.toLowerCase().includes(q) || emp.department?.toLowerCase().includes(q)
+              }).map((emp: any) => (
                 <label key={emp.employeeId} className="flex items-center gap-2 px-3 py-2 hover:bg-gray-50 cursor-pointer">
                   <input type="checkbox" checked={selectedEmployeeIds.has(emp.employeeId)} onChange={() => toggleEmployee(emp.employeeId)} />
                   <span className="text-sm">{emp.name}</span>