feat(api): load .env file directly within app dependencies

Modifies the `AppDependencies` singleton to use the `dotenv` package to load environment variables from the `.env` file at the start of its initialization sequence.

This makes the application's configuration self-contained and resilient, removing the reliance on the `dart_frog_cli` to manage the environment.

Author: fulleni

lib/src/config/app_dependencies.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 
+import 'package:dotenv/dotenv.dart' as dotenv;
 import 'package:ht_api/src/config/database_connection.dart';
 import 'package:ht_api/src/rbac/permission_service.dart';
 import 'package:ht_api/src/services/auth_service.dart';
@@ -82,6 +83,10 @@ class AppDependencies {
   }
 
   Future<void> _init() async {
+    // 0. Load environment variables from .env file.
+    dotenv.load();
+    _log.info('Environment variables loaded from .env file.');
+
     // 1. Establish Database Connection.
     await DatabaseConnectionManager.instance.init();
     final connection = await DatabaseConnectionManager.instance.connection;