Add ripple effect to text-copy action

Generally the use of GestureDetector is discouraged in favor of InkWell
unless you have a very specific reason to use it. InkWells automatically
generate ripple effects if there is a parent material widget in the tree
to indicate to a user that a given widget is interactible.

lib/widgets/messages/message_text.dart

@@ -12,7 +12,8 @@ class MessageText extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return GestureDetector(
+    return InkWell(
+      borderRadius: BorderRadius.circular(16),
       onLongPress: () async {
         await Clipboard.setData(ClipboardData(text: message.content));
         if (context.mounted) {