优化: 添加员工弹窗合同和试用期智能计算

1. 缺省入职日期和合同开始日期为今天，签订日期默认空（留空表示尚未签订）
2. 签约时长与合同结束日期双向自动计算：改年限→算结束日期，改结束日期→算年限
3. 开始日期变更时自动重算结束日期
4. 试用期长度按劳动合同法第19条校验（3月以下不得约定，1年以下≤1月，3年以下≤2月，3年以上≤6月）
5. 有试用期时试用期工资必填，且不得低于转正工资80%（劳动合同法第20条）
6. 校验不通过时禁止保存并显示错误提示

frontend/src/pages/Roster.tsx

@@ -922,15 +922,96 @@ function AddEmployeeModal({ onClose, onSubmit, loading, error }: {
   loading: boolean
   error: any
 }) {
+  const todayStr = new Date().toISOString().slice(0, 10)
+  const defaultEndDate = (() => {
+    const d = new Date()
+    d.setFullYear(d.getFullYear() + 3)
+    d.setDate(d.getDate() - 1)
+    return d.toISOString().slice(0, 10)
+  })()
   const [form, setForm] = useState({
-    name: '', department: '', hireDate: '', monthlySalary: '',
+    name: '', department: '', hireDate: todayStr, monthlySalary: '',
     gender: '男' as '男' | '女', phone: '',
     isPregnant: false, isInMedicalPeriod: false, isWorkInjured: false,
     contractType: 'FIXED' as 'FIXED' | 'UNFIXED' | 'UNSIGNED',
-    signDate: '', startDate: '', endDate: '',
+    signDate: '', startDate: todayStr, endDate: defaultEndDate,
     contractYears: 3, probationMonths: 0, probationSalary: 0,
   })
 
+  // 计算合同月数
+  const contractMonths = (() => {
+    if (form.contractType !== 'FIXED' || !form.startDate) return 0
+    if (form.endDate) {
+      const start = new Date(form.startDate)
+      const end = new Date(form.endDate)
+      return Math.round((end.getTime() - start.getTime()) / (1000 * 60 * 60 * 24 * 30.44))
+    }
+    return form.contractYears * 12
+  })()
+
+  // 试用期上限（劳动合同法第19条）
+  const probationMax = (() => {
+    if (contractMonths >= 36) return 6
+    if (contractMonths >= 12) return 2
+    if (contractMonths >= 3) return 1
+    return 0
+  })()
+
+  const probationError = (() => {
+    if (form.probationMonths <= 0) return ''
+    if (contractMonths > 0 && contractMonths < 3) return '合同不足3个月，不得约定试用期'
+    if (form.probationMonths > probationMax) return `合同${contractMonths}个月，试用期最多${probationMax}个月`
+    return ''
+  })()
+
+  const monthlySalaryNum = parseFloat(form.monthlySalary) || 0
+  const probationSalaryError = (() => {
+    if (form.probationMonths <= 0) return ''
+    if (form.probationSalary <= 0) return '有试用期时试用期工资必填'
+    if (monthlySalaryNum > 0 && form.probationSalary < monthlySalaryNum * 0.8) {
+      return `试用期工资不得低于转正工资的80%（最低¥${(monthlySalaryNum * 0.8).toFixed(0)}）`
+    }
+    return ''
+  })()
+
+  // 合同结束日期自动计算
+  const handleContractYearsChange = (years: number) => {
+    if (!form.startDate || years <= 0) {
+      setForm({ ...form, contractYears: years, endDate: '' })
+      return
+    }
+    const start = new Date(form.startDate)
+    const end = new Date(start)
+    end.setFullYear(end.getFullYear() + years)
+    end.setDate(end.getDate() - 1)
+    setForm({ ...form, contractYears: years, endDate: end.toISOString().slice(0, 10) })
+  }
+
+  // 合同结束日期变更 → 自动计算签约年限
+  const handleEndDateChange = (endDate: string) => {
+    if (!form.startDate || !endDate) {
+      setForm({ ...form, endDate, contractYears: 0 })
+      return
+    }
+    const start = new Date(form.startDate)
+    const end = new Date(endDate)
+    const months = Math.round((end.getTime() - start.getTime()) / (1000 * 60 * 60 * 24 * 30.44))
+    setForm({ ...form, endDate, contractYears: Math.max(1, Math.round(months / 12)) })
+  }
+
+  // 开始日期变更 → 重新计算结束日期
+  const handleStartDateChange = (startDate: string) => {
+    if (form.contractType === 'FIXED' && form.contractYears > 0 && startDate) {
+      const start = new Date(startDate)
+      const end = new Date(start)
+      end.setFullYear(end.getFullYear() + form.contractYears)
+      end.setDate(end.getDate() - 1)
+      setForm({ ...form, startDate, endDate: end.toISOString().slice(0, 10) })
+    } else {
+      setForm({ ...form, startDate })
+    }
+  }
+
   const handleSubmit = () => {
     const data: any = {
       name: form.name, department: form.department,
@@ -951,6 +1032,10 @@ function AddEmployeeModal({ onClose, onSubmit, loading, error }: {
     onSubmit(data)
   }
 
+  const canSubmit = form.name && form.department && form.hireDate && form.monthlySalary
+    && (form.contractType === 'UNSIGNED' || form.startDate)
+    && !probationError && !probationSalaryError
+
   return (
     <Modal open onClose={onClose} title="添加员工">
       <div className="space-y-3">
@@ -978,28 +1063,58 @@ function AddEmployeeModal({ onClose, onSubmit, loading, error }: {
         </div>
         <div className="border-t pt-3">
           <Label>合同类型</Label>
-          <Select value={form.contractType} onChange={(e) => setForm({ ...form, contractType: e.target.value as any })}>
+          <Select value={form.contractType} onChange={(e) => setForm({ ...form, contractType: e.target.value as any, endDate: e.target.value === 'UNFIXED' ? '' : form.endDate })}>
             <option value="FIXED">固定期限</option><option value="UNFIXED">无固定期限</option><option value="UNSIGNED">未签合同</option>
           </Select>
         </div>
         {form.contractType !== 'UNSIGNED' && (
           <div className="space-y-3">
             <div className="grid grid-cols-2 gap-3">
-              <div><Label>签订日期</Label><Input type="date" value={form.signDate} onChange={(e) => setForm({ ...form, signDate: e.target.value })} /></div>
-              <div><Label>合同开始日期 *</Label><Input type="date" value={form.startDate} onChange={(e) => setForm({ ...form, startDate: e.target.value })} /></div>
+              <div>
+                <Label>签订日期</Label>
+                <Input type="date" value={form.signDate} onChange={(e) => setForm({ ...form, signDate: e.target.value })} />
+                <div className="text-xs text-gray-400 mt-0.5">留空表示尚未签订</div>
+              </div>
+              <div><Label>合同开始日期 *</Label><Input type="date" value={form.startDate} onChange={(e) => handleStartDateChange(e.target.value)} /></div>
             </div>
             {form.contractType === 'FIXED' && (
-              <div className="grid grid-cols-3 gap-3">
-                <div><Label>合同结束日期</Label><Input type="date" value={form.endDate} onChange={(e) => setForm({ ...form, endDate: e.target.value })} /></div>
-                <div><Label>试用期(月)</Label><Input type="number" value={form.probationMonths} onChange={(e) => setForm({ ...form, probationMonths: parseInt(e.target.value) || 0 })} min={0} max={6} /></div>
-                <div><Label>试用期工资</Label><Input type="number" value={form.probationSalary} onChange={(e) => setForm({ ...form, probationSalary: parseInt(e.target.value) || 0 })} /></div>
-              </div>
+              <>
+                <div className="grid grid-cols-2 gap-3">
+                  <div>
+                    <Label>签约时长（年）</Label>
+                    <Input type="number" value={form.contractYears} onChange={(e) => handleContractYearsChange(parseInt(e.target.value) || 0)} min={1} />
+                  </div>
+                  <div>
+                    <Label>合同结束日期</Label>
+                    <Input type="date" value={form.endDate} onChange={(e) => handleEndDateChange(e.target.value)} />
+                  </div>
+                </div>
+                <div className="text-xs text-gray-400">修改签约时长自动计算结束日期，修改结束日期自动计算签约时长</div>
+              </>
             )}
+            <div className="grid grid-cols-2 gap-3">
+              <div>
+                <Label>试用期（月）</Label>
+                <Input type="number" value={form.probationMonths} onChange={(e) => setForm({ ...form, probationMonths: parseInt(e.target.value) || 0 })} min={0} max={6} />
+                {contractMonths > 0 && (
+                  <div className="text-xs text-gray-400 mt-0.5">法定上限：{probationMax}个月</div>
+                )}
+                {probationError && <div className="text-xs text-danger mt-0.5">{probationError}</div>}
+              </div>
+              <div>
+                <Label>试用期工资{form.probationMonths > 0 ? ' *' : ''}</Label>
+                <Input type="number" value={form.probationSalary} onChange={(e) => setForm({ ...form, probationSalary: parseFloat(e.target.value) || 0 })} disabled={form.probationMonths <= 0} />
+                {monthlySalaryNum > 0 && form.probationMonths > 0 && (
+                  <div className="text-xs text-gray-400 mt-0.5">不低于转正工资80%（≥¥{(monthlySalaryNum * 0.8).toFixed(0)}）</div>
+                )}
+                {probationSalaryError && <div className="text-xs text-danger mt-0.5">{probationSalaryError}</div>}
+              </div>
+            </div>
           </div>
         )}
         <div className="flex justify-end gap-2 pt-2">
           <Button variant="secondary" onClick={onClose}>取消</Button>
-          <Button onClick={handleSubmit} disabled={loading || !form.name || !form.department || !form.hireDate || !form.monthlySalary}>{loading ? '保存中...' : '保存'}</Button>
+          <Button onClick={handleSubmit} disabled={loading || !canSubmit}>{loading ? '保存中...' : '保存'}</Button>
         </div>
       </div>
     </Modal>