feat: implement API client with JSON handling and error mapping; enhance routing and state management in app shell

flutter/lib/core/router/app_router.dart

@@ -1,24 +1,63 @@
+import 'package:flutter/widgets.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
+
+import '../../core/ui/app_shell.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';
 
 final appRouterProvider = Provider<GoRouter>((ref) {
+  final authState = ref.watch(authStateProvider);
+
   return GoRouter(
-    initialLocation: '/login',
+    initialLocation: '/',
+    redirect: (context, state) {
+      final isLoading = authState.isLoading;
+      final token = authState.valueOrNull;
+      final isLoggedIn = token != null && token.isNotEmpty;
+      final isLoginRoute = state.matchedLocation == '/login';
+      final isRootRoute = state.matchedLocation == '/';
+
+      if (isLoading) {
+        return null;
+      }
+
+      if (isRootRoute) {
+        return isLoggedIn ? '/recipes' : '/login';
+      }
+
+      if (!isLoggedIn && !isLoginRoute) {
+        return '/login';
+      }
+
+      if (isLoggedIn && isLoginRoute) {
+        return '/recipes';
+      }
+
+      return null;
+    },
     routes: [
+      GoRoute(path: '/', builder: (context, state) => const SizedBox.shrink()),
       GoRoute(
         path: '/login',
         builder: (context, state) => const LoginScreen(),
       ),
-      GoRoute(
-        path: '/recipes',
-        builder: (context, state) => const RecipesScreen(),
-      ),
-      GoRoute(
-        path: '/profile',
-        builder: (context, state) => const ProfileScreen(),
+      ShellRoute(
+        builder: (context, state, child) {
+          return AppShell(location: state.uri.path, child: child);
+        },
+        routes: [
+          GoRoute(
+            path: '/recipes',
+            builder: (context, state) => const RecipesScreen(),
+          ),
+          GoRoute(
+            path: '/profile',
+            builder: (context, state) => const ProfileScreen(),
+          ),
+        ],
       ),
     ],
   );