implemented comprehensive accessibility (A11y) support across the app

lib/view/pages/files/sharing/share_options_sheet.dart

@@ -239,6 +239,7 @@ class _ShareOptionsBodyState extends State<_ShareOptionsBody> {
               ),
               trailing: IconButton(
                 onPressed: () => copyToClipboard(context, _share.url!),
+                tooltip: 'Link kopieren',
                 icon: const Icon(Icons.copy_outlined),
               ),
             ),