自选项目实验优化

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

@@ -18,6 +18,9 @@ public sealed class ExperimentProject : EntityBase
     public string? Requirements { get; set; }
     public DateOnly StartDate { get; set; }
     public DateOnly EndDate { get; set; }
+    // 自主预约项目可单独控制学生可选场次的时间窗口（UTC 时刻）。
+    public DateTime? SelectionStartsAt { get; set; }
+    public DateTime? SelectionEndsAt { get; set; }
     public ExperimentProjectStatus Status { get; set; } =
         ExperimentProjectStatus.Draft;
     public DateTime? PublishedAt { get; set; }
@@ -43,6 +46,15 @@ public sealed class ExperimentSession : EntityBase
         ExperimentSessionStatus.Scheduled;
     public DateTime? CancelledAt { get; set; }
     public ICollection<ExperimentBooking> Bookings { get; set; } = [];
+    public ICollection<ExperimentSessionInstructor> Instructors { get; set; } = [];
+}
+
+public sealed class ExperimentSessionInstructor : EntityBase
+{
+    public Guid ExperimentSessionId { get; set; }
+    public ExperimentSession? ExperimentSession { get; set; }
+    public Guid TeacherId { get; set; }
+    public Teacher? Teacher { get; set; }
 }
 
 public sealed class ExperimentBooking : EntityBase