fix(admin): 修复日期选择器与选曲日期的 UTC 时差错位

根本原因: 使用 toISOString().split('T')[0] 会按 UTC 时区截断日期,
在 UTC+8 时区下,本地 00:00~07:59 期间会少 1 天,导致:
- AdminDatePicker/AdminMultiDatePicker 横向条、月历选中值错位
- ScheduleManager selectedDate 今日初始化与今日排期过滤错位
- 月历今日高亮与实际日期不匹配

修复方法: 所有 YYYY-MM-DD 格式化统一使用本地时区的
getFullYear/getMonth/getDate + pad, addDays 前先 setHours(0,0,0,0) 归零
避免 DST 与时区偏移导致的跨天误差

app/components/Admin/ScheduleManager.vue

@@ -974,7 +974,9 @@ const defaultAutoConfig: AutoConfig = {
 
 // 响应式数据
 const showCardGenerator = ref(false)
-const selectedDate = ref(new Date().toISOString().split('T')[0])
+const _pad = (n) => n.toString().padStart(2, '0')
+const _today = new Date(); _today.setHours(0, 0, 0, 0)
+const selectedDate = ref(`${_today.getFullYear()}-${_pad(_today.getMonth() + 1)}-${_pad(_today.getDate())}`)
 const loading = ref(false)
 const songSortOption = ref<AutoConfig['songSortOption']>('votes-desc')
 const hasChanges = ref(false)
@@ -1695,17 +1697,22 @@ const updateLocalScheduledSongs = () => {
   console.log('公开排期数量:', publicSchedules.value.length)
   console.log('草稿数量:', drafts.value.length)
 
-  // 获取已发布的排期
+  const _fmtLocal = (d) => {
+  const x = new Date(d)
+  return `${x.getFullYear()}-${_pad(x.getMonth() + 1)}-${_pad(x.getDate())}`
+}
+
+// 获取已发布的排期
   const todaySchedules = publicSchedules.value.filter((s) => {
     if (!s.playDate) return false
-    const scheduleDateStr = new Date(s.playDate).toISOString().split('T')[0]
+    const scheduleDateStr = _fmtLocal(s.playDate)
     return scheduleDateStr === selectedDate.value
   })
 
   // 获取草稿排期
   const todayDrafts = drafts.value.filter((draft) => {
     if (!draft.playDate) return false
-    const draftDateStr = new Date(draft.playDate).toISOString().split('T')[0]
+    const draftDateStr = _fmtLocal(draft.playDate)
     return draftDateStr === selectedDate.value
   })
 
@@ -2210,7 +2217,7 @@ const confirmMoveDate = async () => {
   const sourceDate = selectedDate.value
   const sourceSchedules = [...publicSchedules.value, ...drafts.value].filter((schedule) => {
     if (!schedule.playDate) return false
-    return new Date(schedule.playDate).toISOString().split('T')[0] === sourceDate
+    return _fmtLocal(schedule.playDate) === sourceDate
   })
 
   if (sourceSchedules.length === 0) {