add main menu and scene manager

core/scene_manager/scene_manager.gd

@@ -0,0 +1,43 @@
+extends CanvasLayer
+
+@export var config: SceneConfig
+@onready var color_rect = $ColorRect
+@onready var loading_screen = $LoadingScreen
+@export var transition_duration: float = 1
+
+func _ready() -> void:
+	color_rect.color.a = 0.0
+	color_rect.mouse_filter = Control.MOUSE_FILTER_IGNORE
+	loading_screen.hide()
+
+func change_scene(scene_enum: SceneConfig.SceneName) -> void:
+	if not config or not config.scenes.has(scene_enum):
+		return
+
+	var target_scene: PackedScene = config.scenes[scene_enum]
+
+	color_rect.mouse_filter = Control.MOUSE_FILTER_STOP
+	
+	var tween_in = create_tween()
+	tween_in.tween_property(color_rect, "color:a", 1.0, transition_duration)
+	await tween_in.finished
+
+	loading_screen.show()
+	await get_tree().process_frame 
+
+	get_tree().change_scene_to_packed(target_scene)
+
+	loading_screen.hide()
+
+	var tween_out = create_tween()
+	tween_out.tween_property(color_rect, "color:a", 0.0, transition_duration)
+	await tween_out.finished
+
+	color_rect.mouse_filter = Control.MOUSE_FILTER_IGNORE
+
+func quit_game() -> void:
+	color_rect.mouse_filter = Control.MOUSE_FILTER_STOP
+	var tween = create_tween()
+	tween.tween_property(color_rect, "color:a", 1.0, transition_duration)
+	await tween.finished
+	get_tree().quit()