重构管理界面为通用标签面板

- 移除 DisciplePanel，改用可复用的 ManagerPanel 占位标签（×4）
- 新增 InventoryPanel 并接入管理页第 5 个标签
- 新增炼丹、外务、订单等子面板占位场景与资源样式
- 样式资源重命名：disciple_info_* 改为 manager_info_*

src/UI/Panels/Manager/InventoryPanel/InventoryPanel.tscn

@@ -0,0 +1,23 @@
+[gd_scene format=3 uid="uid://dxij6vexu5m1q"]
+
+[node name="InventoryPanel" type="Control" unique_id=735363118]
+layout_mode = 3
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+
+[node name="ScrollContainer" type="ScrollContainer" parent="." unique_id=887058553]
+layout_mode = 1
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+
+[node name="Tree" type="Tree" parent="ScrollContainer" unique_id=1018260768]
+layout_mode = 2
+size_flags_horizontal = 3
+size_flags_vertical = 3
+columns = 5