validateMobile static method
Validates a 10-digit mobile number. Returns null if valid, otherwise an error message.
Implementation
static String? validateMobile(String? value) {
if (value == null || value.isEmpty) return 'Mobile number is required';
final mobileRegex = RegExp(r'^\d{10}$');
if (!mobileRegex.hasMatch(value)) return 'Enter a valid 10-digit mobile number';
return null;
}