game: add minimal main menu

scenes/main_menu.gd

@@ -0,0 +1,19 @@
+extends Control
+
+const MAIN = preload("res://scenes/main.tscn")
+
+
+func _ready() -> void:
+	pass
+
+
+func _on_new_game_button_pressed() -> void:
+	get_tree().change_scene_to_packed(MAIN)
+
+
+func _on_options_button_pressed() -> void:
+	pass  # Replace with function body.
+
+
+func _on_exit_game_button_pressed() -> void:
+	get_tree().quit()