Add player controller, state management, and input handling

- Implemented PlayerController.cs to manage player movement and actions.
- Created PlayerState.cs to track player lives, coins, and key status.
- Added CameraFollow.cs for smooth camera movement following the player.
- Developed Character.cs as an abstract class for character behavior.
- Introduced Enums.cs for defining TreasureType and MapElementType.
- Added IDoor interface for door interactions.
- Created InputActions.cs for handling player input actions.
- Implemented MainMenu.cs for basic menu functionality including play and exit options.

Assets/Scripts/Environment/KeyChest.cs

@@ -0,0 +1,37 @@
+using UnityEngine;
+
+public class KeyChest : MonoBehaviour
+{
+    private bool _isOpened = false;
+
+    private void OnTriggerEnter2D(Collider2D collider)
+    {
+        if (_isOpened)
+            return;
+
+        var playerState = collider.GetComponent<PlayerState>();
+        if (playerState != null)
+        {
+            _isOpened = true;
+
+            // Update player state
+            playerState.SetKey();
+
+            // Notify GameManager of key collection
+            if (GameManager.Instance != null)
+            {
+                GameManager.Instance.SetKeyState(true);
+            }
+
+            // Notify LevelManager of key collection
+            if (LevelManager.Instance != null)
+            {
+                LevelManager.Instance.NotifyKeyCollected();
+            }
+
+            // Destroy the chest
+            Destroy(gameObject);
+        }
+    }
+}
+