macos: set id on nested terminal splits

This fixes https://github.com/mitchellh/ghostty/issues/761 for terminal
splits that are not at the root.

macos/Sources/Ghostty/Ghostty.TerminalSplit.swift

@@ -345,6 +345,7 @@ extension Ghostty {
         let neighbors: SplitNode.Neighbors
 
         var body: some View {
+            Group {
                 switch (node) {
                 case nil:
                     Color(.clear)
@@ -373,6 +374,8 @@ extension Ghostty {
                     )
                 }
             }
+            .id(node)
+        }
     }
     
     /// When changing the split state, or going full screen (native or non), the terminal view