feat: add profile screen and update routing; enhance login validation and logout functionality

flutter/lib/features/auth/presentation/login_screen.dart

@@ -22,6 +22,9 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
   }
 
   Future<void> _submit() async {
+    if (_usernameCtrl.text.trim().isEmpty || _passwordCtrl.text.isEmpty) {
+      return;
+    }
     await ref.read(authStateProvider.notifier).login(
           _usernameCtrl.text.trim(),
           _passwordCtrl.text,
@@ -47,12 +50,15 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
             TextField(
               controller: _usernameCtrl,
               decoration: const InputDecoration(labelText: 'Anvandarnamn'),
+              textInputAction: TextInputAction.next,
             ),
             const SizedBox(height: 12),
             TextField(
               controller: _passwordCtrl,
               decoration: const InputDecoration(labelText: 'Lösenord'),
               obscureText: true,
+              textInputAction: TextInputAction.done,
+              onSubmitted: (_) => _submit(),
             ),
             const SizedBox(height: 24),
             if (authState is AsyncLoading)