feat: HUD 增加时间流速控制，新增 Settings 持久化

- 顶栏改为暂停/1x/5x/20x 按钮组，当前档位高亮
- TimeSystem 支持暂停与档位切换
- 新增 Settings 单例，存档默认流速并开机应用
- GameState 补充年月日，支持 12x30 历法推进

src/UI/HUD/top_bar_hud.gd

@@ -2,7 +2,31 @@ extends Control
 
 signal sign_return_mainmenu
 
+const SPEED_BUTTONS := ["Button_Speed1", "Button_Speed5", "Button_Speed20"]
+const ACTIVE_COLOR := Color(1.0, 1.0, 1.0)
+const INACTIVE_COLOR := Color(0.55, 0.55, 0.55)
+
+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))
+	_update_speed_ui()
 
 func _on_button_return_button_up() -> void:
 	sign_return_mainmenu.emit()
-	pass # Replace with function body.
+
+func _on_button_pause_button_up() -> void:
+	TimeSystem.toggle_pause()
+	_update_speed_ui()
+
+func _on_speed_button_up(index: int) -> void:
+	TimeSystem.set_speed_index(index)
+	_update_speed_ui()
+
+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])
+		var active := (i == TimeSystem.speed_index) and not TimeSystem.paused
+		btn.modulate = ACTIVE_COLOR if active else INACTIVE_COLOR