fix(api): centralize and correct dotenv loading in EnvironmentConfig

Refactors environment variable handling to be self-contained within the `EnvironmentConfig` class.

- `EnvironmentConfig` now creates a static `DotEnv` instance, loads the `.env` file, and all getters now read from this instance instead of `Platform.environment`.
- This ensures that environment variables are loaded and read correctly from a single, reliable source, resolving the issue where variables were not available to the application.

Author: fulleni

lib/src/config/environment_config.dart

@@ -1,5 +1,6 @@
 import 'dart:io';
 import 'package:logging/logging.dart';
+import 'package:dotenv/dotenv.dart';
 
 /// {@template environment_config}
 /// A utility class for accessing environment variables.
@@ -9,20 +10,25 @@ import 'package:logging/logging.dart';
 /// connection strings are managed outside of the source code.
 /// {@endtemplate}
 abstract final class EnvironmentConfig {
-  /// Retrieves the PostgreSQL database connection URI from the environment.
   static final _log = Logger('EnvironmentConfig');
+
+  // The DotEnv instance that loads the .env file and platform variables.
+  // It's initialized once and reused.
+  static final _env = DotEnv(includePlatformEnvironment: true)..load();
+
+  /// 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'];
+    final dbUrl = _env['DATABASE_URL'];
     if (dbUrl == null || dbUrl.isEmpty) {
       _log.severe(
         'DATABASE_URL not found. Dumping available environment variables:',
       );
-      Platform.environment.forEach((key, value) {
+      _env.map.forEach((key, value) {
         _log.severe('  - $key: $value');
       });
       throw StateError(
@@ -37,5 +43,5 @@ abstract final class EnvironmentConfig {
   ///
   /// 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';
+  static String get environment => _env['ENV'] ?? 'production';
 }