macos: add ErrorView

macos/Sources/ErrorView.swift

@@ -0,0 +1,24 @@
+import SwiftUI
+
+struct ErrorView: View {
+    var body: some View {
+        HStack {
+            Image("AppIconImage")
+                .resizable()
+                .scaledToFit()
+                .frame(width: 128, height: 128)
+            
+            VStack(alignment: .leading) {
+                Text("Oh, no. 😭").font(.title)
+                Text("Something went fatally wrong.\nCheck the logs and restart Ghostty.")
+            }
+        }
+        .padding()
+    }
+}
+
+struct ErrorView_Previews: PreviewProvider {
+    static var previews: some View {
+        ErrorView()
+    }
+}