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/Infrastructure/Persistence/AppDbContext.cs

@@ -77,6 +77,7 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
     public DbSet<EvaluationRecord> EvaluationRecords => Set<EvaluationRecord>();
     public DbSet<EvaluationScore> EvaluationScores => Set<EvaluationScore>();
     public DbSet<Notification> Notifications => Set<Notification>();
+    public DbSet<MessageDispatch> MessageDispatches => Set<MessageDispatch>();
     public DbSet<StudentStatusChange> StudentStatusChanges =>
         Set<StudentStatusChange>();
     public DbSet<GraduationAuditBatch> GraduationAuditBatches =>
@@ -919,7 +920,23 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
             entity.Property(x => x.Content).HasMaxLength(1000);
             entity.Property(x => x.LinkUrl).HasMaxLength(300);
             entity.HasIndex(x => new { x.UserId, x.IsRead });
+            entity.HasIndex(x => new { x.UserId, x.Category, x.CreatedAt });
+            entity.HasIndex(x => x.MessageDispatchId);
             entity.HasIndex(x => x.CreatedAt);
+            entity.HasOne(x => x.MessageDispatch)
+                .WithMany(x => x.Notifications)
+                .HasForeignKey(x => x.MessageDispatchId)
+                .OnDelete(DeleteBehavior.Cascade);
+        });
+
+        builder.Entity<MessageDispatch>(entity =>
+        {
+            entity.Property(x => x.SenderName).HasMaxLength(100);
+            entity.Property(x => x.Title).HasMaxLength(200);
+            entity.Property(x => x.Content).HasMaxLength(1000);
+            entity.Property(x => x.AudienceName).HasMaxLength(200);
+            entity.Property(x => x.LinkUrl).HasMaxLength(300);
+            entity.HasIndex(x => new { x.SenderUserId, x.CreatedAt });
         });
 
         builder.Entity<AuditLog>(entity =>