成绩通知：仅在某门课程成绩正式发布后自动发送，按成绩单学生名单通知，不展示具体分数；发布状态与通知同一次提交。

手动发信：移除“成绩通知”选项，只能发送普通通知，原有角色与范围权限保持不变。
选课通知：管理员关闭一轮选课时，自动向每位参与学生发送一条汇总通知，包含最终选中课程及候补未成功课程；候补失效、轮次关闭和通知生成保持原子性。
关闭选课界面会明确提示发送通知，并显示实际通知人数。

src/Jiaowu.Api/Domain/Academic/NotificationEntities.cs

@@ -7,6 +7,42 @@ public sealed class Notification : EntityBase
     public Guid UserId { get; set; }
     public required string Title { get; set; }
     public required string Content { get; set; }
+    public NotificationCategory Category { get; set; } = NotificationCategory.General;
     public bool IsRead { get; set; }
     public string? LinkUrl { get; set; }
+    public Guid? MessageDispatchId { get; set; }
+    public MessageDispatch? MessageDispatch { get; set; }
+}
+
+public sealed class MessageDispatch : EntityBase
+{
+    public Guid SenderUserId { get; set; }
+    public required string SenderName { get; set; }
+    public required string Title { get; set; }
+    public required string Content { get; set; }
+    public NotificationCategory Category { get; set; } = NotificationCategory.General;
+    public MessageAudienceType AudienceType { get; set; }
+    public Guid? AudienceId { get; set; }
+    public required string AudienceName { get; set; }
+    public int RecipientCount { get; set; }
+    public string? LinkUrl { get; set; }
+    public ICollection<Notification> Notifications { get; set; } = [];
+}
+
+public enum NotificationCategory
+{
+    General = 1,
+    Approval = 2,
+    Schedule = 3,
+    Grade = 4,
+    Attendance = 5,
+    CourseSelection = 6,
+    Warning = 7
+}
+
+public enum MessageAudienceType
+{
+    School = 1,
+    College = 2,
+    TeachingTask = 3
 }