feat(config): add EnvironmentConfig class for managing environment variables

Author: fulleni

lib/src/config/environment_config.dart

@@ -0,0 +1,33 @@
+import 'dart:io';
+
+/// {@template environment_config}
+/// A utility class for accessing environment variables.
+///
+/// This class provides a centralized way to read configuration values
+/// from the environment, ensuring that critical settings like database
+/// connection strings are managed outside of the source code.
+/// {@endtemplate}
+abstract final class EnvironmentConfig {
+  /// Retrieves the PostgreSQL database connection URI from the environment.
+  ///
+  /// The value is read from the `DATABASE_URL` environment variable.
+  ///
+  /// Throws a [StateError] if the `DATABASE_URL` environment variable is not
+  /// set, as the application cannot function without it.
+  static String get databaseUrl {
+    final dbUrl = Platform.environment['DATABASE_URL'];
+    if (dbUrl == null || dbUrl.isEmpty) {
+      throw StateError(
+        'FATAL: DATABASE_URL environment variable is not set. '
+        'The application cannot start without a database connection.',
+      );
+    }
+    return dbUrl;
+  }
+
+  /// Retrieves the current environment mode (e.g., 'development', 'production').
+  ///
+  /// The value is read from the `ENV` environment variable.
+  /// Defaults to 'production' if the variable is not set.
+  static String get environment => Platform.environment['ENV'] ?? 'production';
+}