added encounter system

Packages/com.jovian.encounter-system/Runtime/SubclassSelectorAttribute.cs

@@ -0,0 +1,9 @@
+using System;
+using UnityEngine;
+
+namespace Jovian.EncounterSystem {
+    /// <summary>Renders a concrete-type picker dropdown for a <c>[SerializeReference]</c> field.</summary>
+    [AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
+    public class SubclassSelectorAttribute : PropertyAttribute {
+    }
+}