Add question bank mastery paths and gap questions

api/QuestionsApi/Models/DashboardModels.cs

@@ -49,6 +49,32 @@ public sealed class DashboardSystemPerformance
     public int Correct { get; set; }
     public int Total { get; set; }
     public int Accuracy { get; set; }
+    public int MasteryScore { get; set; }
+    public string MasteryState { get; set; } = MasteryStates.Unseen;
+    public int DistinctQuestions { get; set; }
+    public int Difficulty4PlusSuccessful { get; set; }
+    public int PendingReviews { get; set; }
+    public DateTime? LastEvidenceUtc { get; set; }
+    public bool RefreshDue { get; set; }
+    public DashboardMasteryAction RecommendedAction { get; set; } = new();
+}
+
+public static class MasteryStates
+{
+    public const string Unseen = "unseen";
+    public const string Learning = "learning";
+    public const string Practicing = "practicing";
+    public const string Strong = "strong";
+    public const string Mastered = "mastered";
+}
+
+public sealed class DashboardMasteryAction
+{
+    public string Type { get; set; } = "practice";
+    public string Label { get; set; } = "Start learning";
+    public int QuestionCount { get; set; } = 10;
+    public int? DifficultyMin { get; set; }
+    public int? DifficultyMax { get; set; }
 }
 
 public sealed class DashboardActivityDay