[auth] Fix QR page back button cropping (#7781)

## Description

Fix buttons getting cropped due to excessive vertical padding.

## Tests

- [x] Verified the change.

Author: ua741

mobile/apps/auth/lib/onboarding/view/setup_enter_secret_key_page.dart

@@ -348,7 +348,7 @@ class _SetupEnterSecretKeyPageState extends State<SetupEnterSecretKeyPage> {
                     width: 400,
                     child: OutlinedButton(
                       style: OutlinedButton.styleFrom(
-                        padding: const EdgeInsets.symmetric(vertical: 8),
+                        padding: const EdgeInsets.symmetric(vertical: 0),
                       ),
                       onPressed: () async {
                         final digits =

mobile/apps/auth/lib/onboarding/view/view_qr_page.dart

@@ -104,7 +104,7 @@ class ViewQrPage extends StatelessWidget {
                     child: Padding(
                       padding: const EdgeInsets.symmetric(
                         horizontal: 16.0,
-                        vertical: 4,
+                        vertical: 0,
                       ),
                       child: Text(l10n.back),
                     ),

mobile/apps/auth/lib/ui/home/home_empty_state.dart

@@ -50,7 +50,7 @@ class HomeEmptyStateWidget extends StatelessWidget {
                         child: OutlinedButton(
                           onPressed: onScanTap,
                           style: OutlinedButton.styleFrom(
-                            padding: const EdgeInsets.symmetric(vertical: 8),
+                            padding: const EdgeInsets.symmetric(vertical: 0),
                           ),
                           child: Text(
                             l10n.importScanQrCode,
@@ -64,7 +64,7 @@ class HomeEmptyStateWidget extends StatelessWidget {
                       child: OutlinedButton(
                         onPressed: onManuallySetupTap,
                         style: OutlinedButton.styleFrom(
-                          padding: const EdgeInsets.symmetric(vertical: 8),
+                          padding: const EdgeInsets.symmetric(vertical: 0),
                         ),
                         child: Text(
                           l10n.importEnterSetupKey,