fix: 允许编辑进行中的拼团/秒杀活动及修复成团检测

- 移除拼团活动"进行中不能修改"限制
- 编辑拼团/秒杀时不再限制开始时间必须晚于当前
- 编辑时日期选择器不禁用过去日期
- 修复JPA缓存导致成团检测失效的问题(clearAutomatically)

flash-sale-frontend/src/pages/admin/flashsales.vue

@@ -275,10 +275,12 @@ const getStockRate = (item: FlashSale) => {
   return Math.round((item.remainingStock / item.flashStock) * 100)
 }
 
-const disablePastDate = (date: Date) => dayjs(date).endOf('day').isBefore(dayjs())
+const disablePastDate = (date: Date) => {
+  if (formMode.value === 'edit') return false
+  return dayjs(date).endOf('day').isBefore(dayjs())
+}
 
 const validateTimeRange = () => {
-  const now = dayjs()
   const startTime = dayjs(form.startTime)
   const endTime = dayjs(form.endTime)
 
@@ -287,7 +289,7 @@ const validateTimeRange = () => {
     return false
   }
 
-  if (!startTime.isAfter(now)) {
+  if (formMode.value === 'create' && !startTime.isAfter(dayjs())) {
     ElMessage.error('开始时间必须晚于当前时间')
     return false
   }

flash-sale-frontend/src/pages/admin/groupbuying.vue

@@ -235,10 +235,12 @@ const getStatusType = (status: string) => {
   }
 }
 
-const disablePastDate = (date: Date) => dayjs(date).endOf('day').isBefore(dayjs())
+const disablePastDate = (date: Date) => {
+  if (editingId.value) return false
+  return dayjs(date).endOf('day').isBefore(dayjs())
+}
 
 const validateTimeRange = () => {
-  const now = dayjs()
   const startTime = dayjs(form.startTime)
   const endTime = dayjs(form.endTime)
 
@@ -247,7 +249,7 @@ const validateTimeRange = () => {
     return false
   }
 
-  if (!startTime.isAfter(now)) {
+  if (!editingId.value && !startTime.isAfter(dayjs())) {
     ElMessage.error('开始时间必须晚于当前时间')
     return false
   }