basic capture functionality

scripts/core/SaveState.cs

@@ -9,6 +9,8 @@ public class SaveState
 	// Respawnables: pickupId -> unixTimeSeconds when it becomes available again
 	public Dictionary<string, long> PickupRespawnAt { get; set; } = new();
 	
+	public HashSet<string> CapturedCreatures { get; set; } = new();
+
 	//public Vector2I? LastPlayerChunk { get; set; } // optional debug, requires "using Godot;"
 	//public int[]? LastPlayerChunk { get; set; }  // [x,y] same debug as above, does not require Godot
 }