补全 UI 设计

- `ItemDescForm` 道具详细信息面板，目前还未添加 DescText 内容的赋值
- `RepoForm` 道具入槽逻辑调整，为了适应 `ItemDescForm` 的点击打开逻辑，点击道具自动匹配槽位改成拖动道具到相应槽位
- 添加了一系列图片素材

Assets/GameMain/Scripts/UI/Game/Context/RepoItemContext.cs

@@ -1,11 +1,13 @@
+using System;
 using GeometryTD.Definition;
 
 namespace GeometryTD.UI
 {
+    [Serializable]
     public class RepoItemContext
     {
-        public string Title;
         public long InstanceId;
+        public bool CanDrag;
         public TowerCompSlotType ComponentSlotType;
         public IconAreaContext IconAreaContext;
     }