feat: enhance routing logic and improve login screen validation; add guarded API call for error handling

flutter/lib/core/api/guarded_api_call.dart

@@ -0,0 +1,18 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import 'api_exception.dart';
+import '../../features/auth/data/auth_providers.dart';
+
+/// Executes [call] and automatically logs out the user if the server
+/// returns 401 Unauthorized. Re-throws the exception so the calling
+/// widget/provider can still display an error if needed.
+Future<T> guardedApiCall<T>(Ref ref, Future<T> Function() call) async {
+  try {
+    return await call();
+  } on ApiException catch (e) {
+    if (e.type == ApiErrorType.unauthorized) {
+      await ref.read(authStateProvider.notifier).logout();
+    }
+    rethrow;
+  }
+}

flutter/lib/core/router/app_router.dart

@@ -1,12 +1,13 @@
-import 'package:flutter/widgets.dart';
+import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
-import '../../core/ui/app_shell.dart';
+import '../ui/app_shell.dart';
+import '../ui/async_state_views.dart';
 import '../../features/auth/data/auth_providers.dart';
-import '../../features/recipes/presentation/recipes_screen.dart';
 import '../../features/auth/presentation/login_screen.dart';
 import '../../features/profile/presentation/profile_screen.dart';
+import '../../features/recipes/presentation/recipes_screen.dart';
 
 final appRouterProvider = Provider<GoRouter>((ref) {
   final authState = ref.watch(authStateProvider);
@@ -17,29 +18,39 @@ final appRouterProvider = Provider<GoRouter>((ref) {
       final isLoading = authState.isLoading;
       final token = authState.valueOrNull;
       final isLoggedIn = token != null && token.isNotEmpty;
-      final isLoginRoute = state.matchedLocation == '/login';
-      final isRootRoute = state.matchedLocation == '/';
+      final location = state.matchedLocation;
+      final isSplash = location == '/';
+      final isLogin = location == '/login';
 
+      // Keep user on splash while auth state is being resolved from storage.
       if (isLoading) {
-        return null;
+        return isSplash ? null : '/';
       }
 
-      if (isRootRoute) {
+      // Redirect away from splash once auth is known.
+      if (isSplash) {
         return isLoggedIn ? '/recipes' : '/login';
       }
 
-      if (!isLoggedIn && !isLoginRoute) {
+      // Unauthenticated user trying to reach a protected route.
+      if (!isLoggedIn && !isLogin) {
         return '/login';
       }
 
-      if (isLoggedIn && isLoginRoute) {
+      // Authenticated user landing on login.
+      if (isLoggedIn && isLogin) {
         return '/recipes';
       }
 
       return null;
     },
     routes: [
-      GoRoute(path: '/', builder: (context, state) => const SizedBox.shrink()),
+      GoRoute(
+        path: '/',
+        builder: (context, state) => const Scaffold(
+          body: LoadingStateView(label: 'Startar...'),
+        ),
+      ),
       GoRoute(
         path: '/login',
         builder: (context, state) => const LoginScreen(),