feat: Favourites support using firmware flags bit 0

- Contact.isFavourite reads bit 0 of firmware flags field
- Toggle favourite via contact action sheet (writes to device)
- Favourites section shown first in contacts tab
- Path size options corrected to [1, 2, 3] bytes

lib/providers/contacts_provider.dart

@@ -342,6 +342,8 @@ class ContactsProvider with ChangeNotifier {
   }
 
   List<Contact> get contacts => _contacts.values.toList();
+  List<Contact> get favouriteContacts =>
+      _contacts.values.where((c) => c.isFavourite).toList();
   List<SavedContactGroup> get savedContactGroups =>
       List<SavedContactGroup>.from(_savedContactGroups)
         ..sort((a, b) => b.createdAt.compareTo(a.createdAt));