isEnvDefinedFalsy function
Check if an environment variable is explicitly set to a falsy value.
Accepts '0', 'false', 'no', 'off' (case-insensitive).
Implementation
bool isEnvDefinedFalsy(dynamic envVar) {
if (envVar == null) return false;
if (envVar is bool) return !envVar;
if (envVar is! String) return false;
if (envVar.isEmpty) return false;
final normalized = envVar.toLowerCase().trim();
return const ['0', 'false', 'no', 'off'].contains(normalized);
}