feat: 社保/公积金缴纳截止日改为按账户配置

- SocialAccount 模型增加 paymentDay 字段
- detectMonthlyTasks 社保/公积金改为按账户 paymentDay 生成提醒
- 账户表单增加缴纳截止日输入
- 设置页面移除社保/公积金缴纳日，保留发薪日和个税日

frontend/src/pages/Settings.tsx

@@ -866,15 +866,11 @@ function NotificationSettings() {
           </label>
           <div className="border-t pt-3 space-y-3">
             <div className="text-xs font-medium">月度事务提醒</div>
-            <div className="text-xs text-gray-500">设置每月截止日，到期后自动生成待办提醒</div>
-            <div className="grid grid-cols-3 gap-3">
+            <div className="text-xs text-gray-500">设置每月截止日，到期后自动生成待办提醒。社保/公积金缴纳日请在对应账户中设置。</div>
+            <div className="grid grid-cols-2 gap-3">
               <div>
-                <Label>社保缴纳日</Label>
-                <Input type="number" min={1} max={28} value={form.socialInsDay ?? 15} onChange={(e) => setForm({ ...form, socialInsDay: Number(e.target.value) })} />
-              </div>
-              <div>
-                <Label>公积金缴纳日</Label>
-                <Input type="number" min={1} max={28} value={form.housingFundDay ?? 15} onChange={(e) => setForm({ ...form, housingFundDay: Number(e.target.value) })} />
+                <Label>发薪日</Label>
+                <Input type="number" min={1} max={28} value={form.payrollDay ?? 10} onChange={(e) => setForm({ ...form, payrollDay: Number(e.target.value) })} />
               </div>
               <div>
                 <Label>个税申报日</Label>

frontend/src/pages/social-insurance/AccountFormModal.tsx

@@ -26,6 +26,7 @@ export function AccountFormModal({ type, account, onClose, onSubmit, saving }: {
   const [bankAccount, setBankAccount] = useState(account?.bankAccount || '')
   const [accountTypeVal, setAccountTypeVal] = useState(account?.accountType || 'BASIC')
   const [isDefault, setIsDefault] = useState(account?.isDefault || false)
+  const [paymentDay, setPaymentDay] = useState(account?.paymentDay || '')
   const [remark, setRemark] = useState(account?.remark || '')
   const [selectedDeptIds, setSelectedDeptIds] = useState<string[]>([])
 
@@ -91,6 +92,11 @@ export function AccountFormModal({ type, account, onClose, onSubmit, saving }: {
           <Label>缴费主体统一社会信用代码</Label>
           <Input value={orgCode} onChange={(e) => setOrgCode(e.target.value)} />
         </div>
+        <div>
+          <Label>每月缴纳截止日</Label>
+          <Input type="number" min={1} max={28} value={paymentDay} onChange={(e) => setPaymentDay(e.target.value)} placeholder="如：15（每月15日前完成缴纳）" />
+          <p className="text-xs text-gray-400 mt-1">设置后，工作台将按此日期生成缴纳提醒</p>
+        </div>
         <div>
           <Label>备注</Label>
           <Input value={remark} onChange={(e) => setRemark(e.target.value)} />
@@ -127,7 +133,7 @@ export function AccountFormModal({ type, account, onClose, onSubmit, saving }: {
           <Button variant="secondary" onClick={onClose}>取消</Button>
           <Button
             disabled={!name || !city || saving}
-            onClick={() => onSubmit({ name, city, accountNo, orgName, orgCode, bankName, bankAccount, accountType: accountTypeVal, isDefault, remark }, selectedDeptIds)}
+            onClick={() => onSubmit({ name, city, accountNo, orgName, orgCode, bankName, bankAccount, accountType: accountTypeVal, paymentDay: paymentDay ? Number(paymentDay) : undefined, isDefault, remark }, selectedDeptIds)}
           >
             {saving ? '保存中...' : '保存'}
           </Button>