Add skill-group prototypes, delete flows, and per-group skill creation UX

RpgRoller/Domain/GameModels.cs

@@ -51,6 +51,9 @@ public sealed class SkillGroup
     public required Guid Id { get; init; }
     public required Guid CharacterId { get; set; }
     public required string Name { get; set; }
+    public required string DiceRollDefinition { get; set; }
+    public required int WildDice { get; set; }
+    public required bool AllowFumble { get; set; }
 }
 
 public sealed class Skill