Add skill groups and GM character owner transfer across stack

RpgRoller/Domain/GameModels.cs

@@ -41,15 +41,23 @@ public sealed class Campaign
 public sealed class Character
 {
     public required Guid Id { get; init; }
-    public required Guid OwnerUserId { get; init; }
+    public required Guid OwnerUserId { get; set; }
     public required Guid CampaignId { get; set; }
     public required string Name { get; set; }
 }
 
+public sealed class SkillGroup
+{
+    public required Guid Id { get; init; }
+    public required Guid CharacterId { get; set; }
+    public required string Name { get; set; }
+}
+
 public sealed class Skill
 {
     public required Guid Id { get; init; }
     public required Guid CharacterId { get; set; }
+    public Guid? SkillGroupId { get; set; }
     public required string Name { get; set; }
     public required string DiceRollDefinition { get; set; }
     public required int WildDice { get; set; }
@@ -70,4 +78,4 @@ public sealed class RollLogEntry
     public required DateTimeOffset TimestampUtc { get; init; }
 }
 
-public sealed record DiceExpression(int DiceCount, int Sides, int Modifier, string Canonical);
+public sealed record DiceExpression(int DiceCount, int Sides, int Modifier, string Canonical);