feat: Add player movement manager, main scene, and backflip animation asset.

scenes/main.tscn

@@ -964,6 +964,7 @@ grow_horizontal = 0
 grow_vertical = 0
 
 [node name="ActionButtonContainer" type="VBoxContainer" parent="ActionMenu"]
+visible = false
 layout_mode = 0
 offset_right = 40.0
 offset_bottom = 40.0
@@ -974,11 +975,13 @@ layout_mode = 2
 text = "Move"
 
 [node name="GrabButton" type="Button" parent="ActionMenu/ActionButtonContainer"]
+visible = false
 custom_minimum_size = Vector2(100, 100)
 layout_mode = 2
 text = "Grab"
 
 [node name="PutButton" type="Button" parent="ActionMenu/ActionButtonContainer"]
+visible = false
 custom_minimum_size = Vector2(100, 100)
 layout_mode = 2
 text = "Put"

scripts/managers/player_movement_manager.gd

@@ -47,13 +47,17 @@ func simple_move_to(grid_position: Vector2i) -> bool:
 	if distance != 1:
 		return false # Only single-step moves allowed
 
+   	# Check if target position is within grid bounds
+	if not enhanced_gridmap.is_position_valid(grid_position):
+		return false
+
 	# Check for finish line logic (delegated back to player or race manager)
 	if player.has_method("can_move_to_finish") and not player.can_move_to_finish(grid_position):
 		return false
 
 	# Check walkability and obstacles
 	var cell_item = enhanced_gridmap.get_cell_item(Vector3i(grid_position.x, 0, grid_position.y))
-	if cell_item in enhanced_gridmap.non_walkable_items or player.is_position_occupied(grid_position): 
+	if cell_item == -1 or cell_item in enhanced_gridmap.non_walkable_items or player.is_position_occupied(grid_position):
 		return false
 	
 	if enhanced_gridmap.is_blocked_by_obstacle(player.current_position, grid_position, 3):
@@ -75,6 +79,10 @@ func move_to_clicked_position(grid_position: Vector2i) -> bool:
 	if not player.is_multiplayer_authority() or is_moving or player.action_points <= 0:
 		return false
 	
+	# Validate grid position is within bounds
+	if not enhanced_gridmap.is_position_valid(grid_position):
+		return false
+	
 	# Check finish line logic
 	if player.has_method("can_move_to_finish") and not player.can_move_to_finish(grid_position):
 		return false