Integrate Nakama managers and enhance powerup system

Added Nakama and related manager scripts to autoload in project.godot and updated input mappings. Improved powerup_manager.gd with new methods and aliases for compatibility and gameplay rewards. Refactored ui_manager.gd to better initialize UI elements and removed unused code. Added playerboard_is_empty to player.gd for board state checks. Minor formatting changes in Nakama C# utility files for consistency.

scenes/player.gd

@@ -645,6 +645,12 @@ func apply_stagger(duration: float = 1.5):
 	else:
 		_apply_tint_recursive(self, Color.WHITE) # Remove tint
 
+func playerboard_is_empty() -> bool:
+	for item in playerboard:
+		if item != -1:
+			return false
+	return true
+
 func drop_random_item():
 	if playerboard_is_empty():
 		return