Implement requested workflow and UI updates

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

@@ -59,6 +59,11 @@ public sealed class CourseSubstitution : EntityBase
     public Course? OriginalCourse { get; set; }
     public Guid SubstituteCourseId { get; set; }
     public Course? SubstituteCourse { get; set; }
+    // The published rule that authorized this exception.  Keeping it on the
+    // application makes later curriculum and audit results explainable even
+    // when course metadata changes.
+    public Guid? CourseEquivalencyRuleId { get; set; }
+    public CourseEquivalencyRule? CourseEquivalencyRule { get; set; }
     public required string Reason { get; set; }
     public ApprovalStatus Status { get; set; } = ApprovalStatus.Submitted;
     public string? ReviewComment { get; set; }
@@ -67,6 +72,21 @@ public sealed class CourseSubstitution : EntityBase
     public Guid? ReviewedByUserId { get; set; }
 }
 
+// A formal, reusable replacement relationship.  Applications may only use an
+// enabled rule; approval remains a student-specific decision.
+public sealed class CourseEquivalencyRule : EntityBase
+{
+    public Guid OriginalCourseId { get; set; }
+    public Course? OriginalCourse { get; set; }
+    public Guid SubstituteCourseId { get; set; }
+    public Course? SubstituteCourse { get; set; }
+    public Guid? MajorId { get; set; }
+    public Major? Major { get; set; }
+    public int? EffectiveGrade { get; set; }
+    public bool IsEnabled { get; set; } = true;
+    public string? Notes { get; set; }
+}
+
 public enum ApprovalStatus
 {
     Submitted = 1,

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

@@ -49,6 +49,10 @@ public sealed class CourseEnrollment : EntityBase
     public EnrollmentType EnrollmentType { get; set; } = EnrollmentType.Normal;
     public DateTime EnrolledAt { get; set; } = DateTime.UtcNow;
     public DateTime? WaitlistedAt { get; set; }
+    // Kept after the queue entry leaves the active list so students and staff
+    // can see why a particular candidate did or did not move forward.
+    public DateTime? WaitlistResolvedAt { get; set; }
+    public string? WaitlistResolutionReason { get; set; }
     public DateTime? WithdrawnAt { get; set; }
 }