refactor: HUD 节点改用唯一名称引用，场景识别改用分组

- TopBarHUD 用 @onready + % 唯一名称替代硬编码路径
- TimeSystem 用 game_scene 分组替代场景名字符串比较

src/UI/HUD/top_bar_hud.gd

@@ -5,24 +5,25 @@ extends Control
 ## 请求返回主菜单。
 signal sign_return_mainmenu
 
-## 三个流速按钮的节点名（与 tscn 中的 SpeedGroup 子节点对应）。
-const SPEED_BUTTONS := ["Button_Speed1", "Button_Speed5", "Button_Speed20"]
 ## 激活档位按钮颜色。
 const ACTIVE_COLOR := Color(1.0, 1.0, 1.0)
 ## 未激活档位按钮颜色。
 const INACTIVE_COLOR := Color(0.55, 0.55, 0.55)
 
+@onready var time_label: Label = %Value_Time
+@onready var pause_button: Button = %Button_Pause
+@onready var speed_buttons: Array[Button] = [%Button_Speed1, %Button_Speed5, %Button_Speed20]
+
 func _ready() -> void:
-	for i in SPEED_BUTTONS.size():
-		var btn: Button = $HBoxContainer/SpeedGroup.get_node(SPEED_BUTTONS[i])
-		btn.button_up.connect(_on_speed_button_up.bind(i))
+	for i in speed_buttons.size():
+		speed_buttons[i].button_up.connect(_on_speed_button_up.bind(i))
 	TimeSystem.day_passed.connect(_on_day_passed)
 	_update_speed_ui()
-	$HBoxContainer/Value_Time.text = TimeSystem.get_date_text()
+	time_label.text = TimeSystem.get_date_text()
 
 ## 每日推进时刷新日期显示。
 func _on_day_passed(_year: int, _month: int, _day: int) -> void:
-	$HBoxContainer/Value_Time.text = TimeSystem.get_date_text()
+	time_label.text = TimeSystem.get_date_text()
 
 ## 点击"返回"按钮。
 func _on_button_return_button_up() -> void:
@@ -41,9 +42,7 @@ func _on_speed_button_up(index: int) -> void:
 
 ## 刷新速度组 UI：暂停按钮文字与各档位高亮状态。
 func _update_speed_ui() -> void:
-	var pause_btn: Button = $HBoxContainer/SpeedGroup/Button_Pause
-	pause_btn.text = "继续" if TimeSystem.paused else "暂停"
-	for i in SPEED_BUTTONS.size():
-		var btn: Button = $HBoxContainer/SpeedGroup.get_node(SPEED_BUTTONS[i])
+	pause_button.text = "继续" if TimeSystem.paused else "暂停"
+	for i in speed_buttons.size():
 		var active := (i == TimeSystem.speed_index) and not TimeSystem.paused
-		btn.modulate = ACTIVE_COLOR if active else INACTIVE_COLOR
+		speed_buttons[i].modulate = ACTIVE_COLOR if active else INACTIVE_COLOR