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

frontend/app/lib/auth/form.dart

@@ -19,7 +19,8 @@ import 'validation.dart';
 import '../generated/i18n/app_localizations.dart';
 
 class AuthForm extends StatefulWidget {
-  const AuthForm({super.key});
+  const AuthForm({super.key, this.email});
+  final String? email;
 
   @override
   State<AuthForm> createState() => _AuthFormState();
@@ -33,7 +34,7 @@ class _AuthFormState extends State<AuthForm> {
   bool _showPassword = false;
   bool _showConfirmation = false;
   bool _submitted = false;
-  final _email = TextEditingController();
+  late final _email = TextEditingController(text: widget.email);
   final _name = TextEditingController();
 
   AuthProvider get _provider =>
@@ -264,6 +265,7 @@ class _AuthFormState extends State<AuthForm> {
                   key: const ValueKey('password'),
                   enabled: !state.isLoading,
                   controller: _password,
+                  autofocus: widget.email?.isNotEmpty ?? false,
                   obscureText: !_showPassword,
                   autofillHints: [
                     _signUp

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),
                         ),
                       ),
                     ],