Complete verification links and preserve verified login email (#60)

frontend/app/lib/auth/page.dart

@@ -10,7 +10,8 @@ import 'form.dart';
 import '../generated/i18n/app_localizations.dart';
 
 class AuthPage extends StatefulWidget {
-  const AuthPage({super.key});
+  const AuthPage({super.key, this.email});
+  final String? email;
 
   @override
   State<AuthPage> createState() => _AuthPageState();
@@ -56,7 +57,7 @@ class _AuthPageState extends State<AuthPage> {
                       Center(
                         child: ConstrainedBox(
                           constraints: const BoxConstraints(maxWidth: 440),
-                          child: AuthForm(key: _formKey),
+                          child: AuthForm(key: _formKey, email: widget.email),
                         ),
                       ),
                     ],