feat(songs): 歌曲管理支持批量驳回、投稿留言自动审查与排期范围可见性过滤

- 新增 /api/admin/songs/batch-reject.post 批量驳回接口（事务清排期/投票/扣接纳数/黑名单去重/异步通知）
- requireSongAdmin 三角色校验 + createApiError 统一错误包装
- scheduleDaysBefore/After 四字段排期可见范围限制（开放 API 与公开排期接口三处缓存路径 + DB 条件过滤）
- submissionNoteAutoModeration 基于黑名单 KEYWORD/LANGUAGE/GENRE 自动判定留言 publicStatus，命中自动关闭 submissionNotePublic
- 更新 songs/request.post 与 songs/[id]/update.put 接入自动审查逻辑

server/utils/grade-class-core.ts

@@ -0,0 +1,36 @@
+export const smartSort = (a: string, b: string) => {
+  const gradeOrder: Record<string, number> = {
+    '初一': 1, '初二': 2, '初三': 3,
+    '高一': 4, '高二': 5, '高三': 6,
+    '大一': 7, '大二': 8, '大三': 9, '大四': 10,
+    '教师': 99, '教职工': 99
+  }
+
+  const weightA = gradeOrder[a]
+  const weightB = gradeOrder[b]
+
+  if (weightA !== undefined && weightB !== undefined) return weightA - weightB
+  if (weightA !== undefined) return -1
+  if (weightB !== undefined) return 1
+
+  return a.localeCompare(b, 'zh-CN', { numeric: true })
+}
+
+export interface GradeClassOption {
+  grade: string
+  class: string
+}
+
+export const resolveGradeClassOptions = (
+  configItems: GradeClassOption[],
+  fallbackItems: GradeClassOption[]
+): GradeClassOption[] => {
+  const source = configItems.length > 0 ? configItems : fallbackItems
+
+  return source
+    .filter((item): item is GradeClassOption => Boolean(item.grade?.trim()) && Boolean(item.class?.trim()))
+    .sort((a, b) => {
+      const gradeResult = smartSort(a.grade, b.grade)
+      return gradeResult || smartSort(a.class, b.class)
+    })
+}