[Refactor] Replace [SerializeField] + getter with [field: SerializeField] auto-properties

Convert serialized private fields with public arrow getters to
[field: SerializeField] auto-properties across ScriptableObjects
(DieDefinitionSO, CategoryDefinition, ModifierDefinition, Effect,
ModifierBehavior, SumOfValueCategory) and select MonoBehaviours
(DiceRoller, Dice.Entry struct). Fields with type-changing getters
(List→IReadOnlyList) or computed getters are intentionally kept as-is.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Assets/Scripts/Dice/Dice.cs

@@ -9,15 +9,12 @@ namespace YachtDice.Dice
         [Serializable]
         public struct Entry : IEquatable<Entry>
         {
-            [SerializeField] private int value;
-            [SerializeField] private Transform point;
+            [field: SerializeField] public int Value { get; private set; }
+            [field: SerializeField] public Transform Point { get; private set; }
 
-            public int Value => value;
-            public Transform Point => point;
-
-            public bool Equals(Entry other) => point == other.point;
+            public bool Equals(Entry other) => Point == other.Point;
             public override bool Equals(object obj) => obj is Entry other && Equals(other);
-            public override int GetHashCode() => point != null ? point.GetHashCode() : 0;
+            public override int GetHashCode() => Point != null ? Point.GetHashCode() : 0;
         }
 
         [SerializeField] private List<Entry> entries = new();