feat: 待签合同支持登记线下签署日期

- 线下手签合同：展开后可点击「登记签署日期」选择日期并保存
  保存后合同从待签列表移除（signDate 已填写）
- 电子签合同：签署日期由电签系统自动回写，不可手动修改
- 后端新增 POST /esign/sign-date 接口
  电子签合同拒绝手动修改签署日期

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

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

frontend/src/pages/ESign.tsx

@@ -788,9 +788,30 @@ function PendingTab({ pendingList, loading, onRemind, remindLoading, remindData,
   remindData: any
   onDetail: (id: string) => void
 }) {
+  const queryClient = useQueryClient()
   const [expandedEmp, setExpandedEmp] = useState<string | null>(null)
   const [remindEmpId, setRemindEmpId] = useState<string | null>(null)
   const [copied, setCopied] = useState(false)
+  const [signDateEditing, setSignDateEditing] = useState<string | null>(null)
+  const [signDateValue, setSignDateValue] = useState('')
+  const [signDateSaving, setSignDateSaving] = useState(false)
+
+  /** 保存签署日期 */
+  const handleSaveSignDate = async (contractId: string) => {
+    if (!signDateValue) { toast.error('请选择签署日期'); return }
+    setSignDateSaving(true)
+    try {
+      await esignApi.signDate(contractId, signDateValue)
+      toast.success('签署日期已登记')
+      setSignDateEditing(null)
+      setSignDateValue('')
+      queryClient.invalidateQueries({ queryKey: ['esign-pending'] })
+    } catch (err: any) {
+      toast.error(err?.response?.data?.error?.message || '登记失败')
+    } finally {
+      setSignDateSaving(false)
+    }
+  }
 
   const handleCopy = (url: string) => {
     navigator.clipboard?.writeText(url)
@@ -908,7 +929,44 @@ function PendingTab({ pendingList, loading, onRemind, remindLoading, remindData,
                                   </button>
                                 )}
                                 {item.type === 'contract' && (
-                                  <span className="text-gray-400 ml-auto">纸质合同未登记签署日期</span>
+                                  <div className="ml-auto flex items-center gap-2">
+                                    {signDateEditing === item.contractId ? (
+                                      <>
+                                        <input
+                                          type="date"
+                                          value={signDateValue}
+                                          onChange={(e) => setSignDateValue(e.target.value)}
+                                          className="h-7 px-2 text-xs border rounded"
+                                        />
+                                        <button
+                                          className="text-xs text-primary hover:underline"
+                                          disabled={signDateSaving}
+                                          onClick={() => handleSaveSignDate(item.contractId)}
+                                        >
+                                          {signDateSaving ? '保存中...' : '保存'}
+                                        </button>
+                                        <button
+                                          className="text-xs text-gray-400 hover:text-gray-600"
+                                          onClick={() => { setSignDateEditing(null); setSignDateValue('') }}
+                                        >
+                                          取消
+                                        </button>
+                                      </>
+                                    ) : (
+                                      <>
+                                        <span className="text-gray-400">未登记签署日期</span>
+                                        <button
+                                          className="text-xs text-primary hover:underline"
+                                          onClick={() => {
+                                            setSignDateEditing(item.contractId)
+                                            setSignDateValue(new Date().toISOString().slice(0, 10))
+                                          }}
+                                        >
+                                          登记签署日期
+                                        </button>
+                                      </>
+                                    )}
+                                  </div>
                                 )}
                               </div>
                             ))}