feat: 添加升级面板到arena，添加全局事件监听升级选择

scenes/arena/spawner.gd

@@ -1,6 +1,8 @@
 extends Node2D
 class_name Spawner
 
+signal on_wave_completed
+
 @export var spawn_area_size := Vector2(1000, 500)
 @export var waves_data: Array[WaveData]
 @export var enemy_collection: Array[UnitStats]
@@ -12,12 +14,6 @@ var wave_index := 1
 var current_wave_data: WaveData
 var spawned_enemies: Array[Enemy] = []
 
-
-# Called when the node enters the scene tree for the first time.
-func _ready() -> void:
-	start_wave()
-
-
 func find_wave_data() -> WaveData:
 	for wave in waves_data:
 		if wave and wave.is_vaild_index(wave_index):
@@ -96,6 +92,7 @@ func _on_spawn_timer_timeout() -> void:
 
 func _on_wave_timer_timeout() -> void:
 	Global.game_paused = true
+	on_wave_completed.emit()
 	spawn_timer.stop()
 	clear_enemies()
 	update_enemies_new_wave()