fix(ui): drop unsupported tonalButtonTheme for Flutter 3.32

Keeps Soft Neutral ThemeData compatible with the web Docker Flutter image.

Co-authored-by: okuma <o0kuma@users.noreply.github.com>

mobile/lib/theme/app_theme.dart

@@ -171,7 +171,6 @@ class AppTheme {
           elevation: 0,
         ),
       ),
-      tonalButtonTheme: null,
       outlinedButtonTheme: OutlinedButtonThemeData(
         style: OutlinedButton.styleFrom(
           foregroundColor: ink,