refactor(*): Restructure game into reusable Arena/GameMode architecture with controller-driven ships, adding Free Play and Match modes

Game/scripts/free_play.gd

@@ -0,0 +1,22 @@
+extends GameMode
+
+# Free Play: one player ship, one ball, no timer, no score — practice like
+# Rocket League's free play. R resets the ball, Esc returns to the menu.
+
+
+func _start() -> void:
+	spawn_ball()
+	var player_ship := spawn_ship(0, 0, PlayerShipController.new())
+	spawn_camera_rig(player_ship)
+
+
+func _on_goal_scored(conceding_team: int) -> void:
+	print("Goal! (into team %d's goal)" % conceding_team)
+	reset_ball()
+
+
+func _unhandled_input(event):
+	if event.is_action_pressed("reset_ball"):
+		reset_ball()
+	else:
+		super(event)