新增存档面板：组/槽两级列表浏览与删除

src/UI/Panels/SaveGroup.tscn

@@ -0,0 +1,25 @@
+[gd_scene format=3 uid="uid://t1jkqpmxb160"]
+
+[ext_resource type="Script" uid="uid://dos00byqj2c7m" path="res://src/UI/Panels/SaveGroup.gd" id="1_j6osu"]
+[ext_resource type="Theme" uid="uid://btnjeju2d47x8" path="res://resources/save_menu_button_theme.tres" id="2_uoetd"]
+
+[node name="SaveGroup" type="HBoxContainer" unique_id=1600113286]
+anchors_preset = 10
+anchor_right = 1.0
+offset_bottom = 29.0
+grow_horizontal = 2
+script = ExtResource("1_j6osu")
+
+[node name="LabelId" type="Button" parent="." unique_id=253528830]
+layout_mode = 2
+size_flags_horizontal = 3
+size_flags_stretch_ratio = 3.0
+text = "A"
+
+[node name="ButtonDel" type="Button" parent="." unique_id=1248721049]
+layout_mode = 2
+size_flags_horizontal = 3
+theme = ExtResource("2_uoetd")
+text = "Del"
+
+[connection signal="button_up" from="ButtonDel" to="." method="_on_button_del_button_up"]