feat(import): implement recipe import functionality with file and URL support

Co-authored-by: Copilot <copilot@github.com>

flutter/lib/core/ui/app_shell.dart

@@ -39,6 +39,12 @@ class AppShell extends ConsumerWidget {
       icon: Icons.storefront_outlined,
       label: 'Baslager',
     ),
+    _AppDestination(
+      path: '/import',
+      title: 'Importera',
+      icon: Icons.upload_file_outlined,
+      label: 'Importera',
+    ),
     _AppDestination(
       path: '/profile',
       title: 'Profil',