macos: text in about window is selectable

Fixes #1163

I also fixed the AppIconImage from being 1024x1024 to much smaller so we
don't see as many artifacts in the downsize.

macos/Assets.xcassets/AppIconImage.imageset/Contents.json

@@ -1,17 +1,17 @@
 {
   "images" : [
     {
-      "filename" : "199110421-9ff5fc30-a244-441e-9882-26070662adf9.png",
+      "filename" : "icon_128x128.png",
       "idiom" : "universal",
       "scale" : "1x"
     },
     {
-      "filename" : "199110421-9ff5fc30-a244-441e-9882-26070662adf9 1.png",
+      "filename" : "icon_128x128@2x@2x.png",
       "idiom" : "universal",
       "scale" : "2x"
     },
     {
-      "filename" : "199110421-9ff5fc30-a244-441e-9882-26070662adf9 2.png",
+      "filename" : "icon_256x256@2x@2x.png",
       "idiom" : "universal",
       "scale" : "3x"
     }

macos/Sources/Features/About/AboutView.swift

@@ -15,10 +15,12 @@ struct AboutView: View {
             
             Text("Ghostty")
                 .font(.title3)
+                .textSelection(.enabled)
             
             if let version = self.version {
                 Text("Version: \(version)")
                     .font(.body)
+                    .textSelection(.enabled)
             }
         }
         .frame(minWidth: 300)