refactor(config): remove use of test-only member in EnvironmentConfig

Removes the iteration over `_env.map` to resolve an `invalid_use_of_visible_for_testing_member` warning. The `.map` getter in the `dotenv` package is intended for testing only.

This change respects the dependency's API contract, making the configuration loading more robust and removing the lint warning. The error message for a missing `DATABASE_URL` remains clear and actionable.

Author: fulleni

lib/src/config/environment_config.dart

@@ -24,12 +24,7 @@ abstract final class EnvironmentConfig {
   static String get databaseUrl {
     final dbUrl = _env['DATABASE_URL'];
     if (dbUrl == null || dbUrl.isEmpty) {
-      _log.severe(
-        'DATABASE_URL not found. Dumping available environment variables:',
-      );
-      _env.map.forEach((key, value) {
-        _log.severe('  - $key: $value');
-      });
+      _log.severe('DATABASE_URL not found in environment variables.');
       throw StateError(
         'FATAL: DATABASE_URL environment variable is not set. '
         'The application cannot start without a database connection.',