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

Game/scripts/arena.gd

@@ -0,0 +1,32 @@
+class_name Arena
+extends Node3D
+
+# A reusable stadium: terrain, lighting, environment, two team goals, and
+# spawn markers. An arena holds no rules and no state — game modes query it
+# for spawn transforms and goals, then spawn ships/ball themselves.
+
+
+func _ready():
+	add_to_group("arena")
+
+
+func get_ball_spawn() -> Transform3D:
+	return $BallSpawn.global_transform
+
+
+func get_ship_spawns(team: int) -> Array[Transform3D]:
+	var spawns: Array[Transform3D] = []
+	var container := get_node_or_null("SpawnsTeam%d" % team)
+	if container:
+		for child in container.get_children():
+			if child is Marker3D:
+				spawns.append(child.global_transform)
+	return spawns
+
+
+func get_goals() -> Array[Goal]:
+	var goals: Array[Goal] = []
+	for child in get_children():
+		if child is Goal:
+			goals.append(child)
+	return goals