Implement requested Jiaowu workflow updates

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

@@ -0,0 +1,40 @@
+using Jiaowu.Api.Domain.Common;
+
+namespace Jiaowu.Api.Domain.Academic;
+
+/// <summary>
+/// 校历中的独立日程。它仅用于展示和提醒，不参与任何业务流程的状态判断或截止限制。
+/// </summary>
+public sealed class AcademicCalendarEvent : EntityBase
+{
+    public Guid AcademicTermId { get; set; }
+    public AcademicTerm? AcademicTerm { get; set; }
+    public required string Title { get; set; }
+    public AcademicCalendarEventKind Kind { get; set; } = AcademicCalendarEventKind.Other;
+    public DateOnly StartsOn { get; set; }
+    public DateOnly? EndsOn { get; set; }
+    public int ReminderDays { get; set; } = 7;
+    public string? AudienceRoles { get; set; }
+    public string? Description { get; set; }
+    public bool IsEnabled { get; set; } = true;
+    public AcademicCalendarEventSource Source { get; set; } = AcademicCalendarEventSource.Manual;
+    public int? SourceYear { get; set; }
+    public bool? IsOffDay { get; set; }
+}
+
+public enum AcademicCalendarEventKind
+{
+    CourseSelection = 1,
+    Grade = 2,
+    Evaluation = 3,
+    Exam = 4,
+    GraduationAudit = 5,
+    PublicHoliday = 6,
+    Other = 99
+}
+
+public enum AcademicCalendarEventSource
+{
+    Manual = 1,
+    HolidayCn = 2
+}