补全防御塔组装与介绍描述功能

- RepoForm.CombineArea：防御塔组装，直接继承所有组件的属性
- ItemDescUtility：根据属性构建不同的 ItemDescForm 的文本

Assets/GameMain/Scripts/UI/Game/View/CombineArea.cs

@@ -1,4 +1,5 @@
 using GeometryTD.Definition;
+using GeometryTD.CustomEvent;
 using UnityEngine;
 using UnityEngine.EventSystems;
 
@@ -42,7 +43,14 @@ namespace GeometryTD.UI
 
         public void OnCombineClick()
         {
-            // TODO: Combine logic.
+            if (!TryGetBoundItemId(TowerCompSlotType.Muzzle, out long muzzleItemId) ||
+                !TryGetBoundItemId(TowerCompSlotType.Bearing, out long bearingItemId) ||
+                !TryGetBoundItemId(TowerCompSlotType.Base, out long baseItemId))
+            {
+                return;
+            }
+
+            GameEntry.Event.Fire(this, RepoCombineRequestedEventArgs.Create(muzzleItemId, bearingItemId, baseItemId));
         }
 
         public bool TryAssignItem(RepoItemContext itemContext)
@@ -127,5 +135,18 @@ namespace GeometryTD.UI
 
             return null;
         }
+
+        private bool TryGetBoundItemId(TowerCompSlotType slotType, out long boundItemId)
+        {
+            boundItemId = 0;
+            CombineSlotItem slot = FindSlot(slotType);
+            if (slot == null || !slot.HasItem || slot.BoundItemId <= 0)
+            {
+                return false;
+            }
+
+            boundItemId = slot.BoundItemId;
+            return true;
+        }
     }
 }