refactor: enhance GameStateStore integration and improve skill management

scripts/State/PlayerState.cs

@@ -11,6 +11,11 @@ public class PlayerState
 {
     private const int DefaultLives = 3;
 
+    /// <summary>
+    /// The level index the player is currently on. Persisted across sessions.
+    /// </summary>
+    public int CurrentLevel { get; set; }
+
     /// <summary>
     /// Saved coins (not including current session).
     /// </summary>
@@ -56,6 +61,7 @@ public class PlayerState
     /// </summary>
     public void Reset()
     {
+        CurrentLevel = 0;
         Coins = 0;
         Lives = DefaultLives;
         CompletedLevels.Clear();