Add environment configuration with flavor support

- Add AppConfig class for dev/prod environment settings
- Create main_dev.dart and main_prod.dart entry points
- Update datasources to use centralized API URL config
- Support --dart-define=ENV for runtime configuration

lib/core/config/app_config.dart

@@ -0,0 +1,55 @@
+/// Application configuration for different environments.
+///
+/// This class provides environment-specific settings like API URLs
+/// and logging levels, supporting both development and production builds.
+class AppConfig {
+  final String apiBaseUrl;
+  final bool enableLogging;
+  final String environment;
+
+  const AppConfig._({
+    required this.apiBaseUrl,
+    required this.enableLogging,
+    required this.environment,
+  });
+
+  /// Development configuration (uses local backend)
+  static const AppConfig dev = AppConfig._(
+    apiBaseUrl: 'http://10.0.2.2:8000', // Android emulator localhost
+    enableLogging: true,
+    environment: 'development',
+  );
+
+  /// Production configuration (Linode VPS)
+  static const AppConfig prod = AppConfig._(
+    apiBaseUrl: 'http://172.104.152.69',
+    enableLogging: false,
+    environment: 'production',
+  );
+
+  /// Current active configuration (set at app startup)
+  static AppConfig _current = dev;
+
+  /// Get the current configuration
+  static AppConfig get current => _current;
+
+  /// Initialize configuration from dart-define or default to dev
+  static void initialize({String? environment}) {
+    const envFromDefine = String.fromEnvironment('ENV', defaultValue: 'dev');
+    final env = environment ?? envFromDefine;
+
+    switch (env) {
+      case 'prod':
+      case 'production':
+        _current = prod;
+        break;
+      case 'dev':
+      case 'development':
+      default:
+        _current = dev;
+    }
+  }
+
+  @override
+  String toString() => 'AppConfig(env: $environment, api: $apiBaseUrl)';
+}

lib/features/auth/data/datasources/auth_remote_datasource.dart

@@ -3,6 +3,7 @@ import 'dart:io';
 
 import 'package:http/http.dart' as http;
 
+import '../../../../core/config/app_config.dart';
 import '../../../../core/errors/exceptions.dart';
 import '../../../../core/logging/app_logger.dart';
 import '../models/token_model.dart';
@@ -29,10 +30,7 @@ class AuthRemoteDataSourceImpl implements AuthRemoteDataSource {
   final AppLogger logger;
   final http.Client _client;
 
-  static const String _baseUrl = String.fromEnvironment(
-    'API_URL',
-    defaultValue: 'http://localhost:8000',
-  );
+  String get _baseUrl => AppConfig.current.apiBaseUrl;
 
   AuthRemoteDataSourceImpl({
     required this.logger,

lib/features/tasks/data/datasources/task_remote_datasource.dart

@@ -3,6 +3,7 @@ import 'dart:io';
 
 import 'package:http/http.dart' as http;
 
+import '../../../../core/config/app_config.dart';
 import '../../../../core/errors/exceptions.dart';
 import '../../../../core/logging/app_logger.dart';
 import '../models/task_model.dart';
@@ -21,10 +22,7 @@ class TaskRemoteDataSourceImpl implements TaskRemoteDataSource {
   final AppLogger logger;
   final http.Client _client;
 
-  static const String _baseUrl = String.fromEnvironment(
-    'API_URL',
-    defaultValue: 'http://localhost:8000',
-  );
+  String get _baseUrl => AppConfig.current.apiBaseUrl;
 
   TaskRemoteDataSourceImpl({
     required this.logger,

lib/main.dart

@@ -1,10 +1,19 @@
 import 'package:flutter/material.dart';
 
 import 'app.dart';
+import 'core/config/app_config.dart';
 import 'core/di/injection_container.dart' as di;
 
+/// Default entry point (uses dart-define ENV or defaults to dev).
+///
+/// Run with: flutter run
+/// Or specify env: flutter run --dart-define=ENV=prod
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
+
+  // Initialize configuration from dart-define (defaults to dev)
+  AppConfig.initialize();
+
   await di.init();
   runApp(const AgendaApp());
 }

lib/main_dev.dart

@@ -0,0 +1,21 @@
+import 'package:flutter/material.dart';
+
+import 'app.dart';
+import 'core/config/app_config.dart';
+import 'core/di/injection_container.dart' as di;
+
+/// Development entry point.
+///
+/// Run with: flutter run -t lib/main_dev.dart
+/// Or with explicit env: flutter run --dart-define=ENV=dev
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+
+  // Initialize development configuration
+  AppConfig.initialize(environment: 'dev');
+
+  // Initialize dependency injection
+  await di.init();
+
+  runApp(const AgendaApp());
+}

lib/main_prod.dart

@@ -0,0 +1,22 @@
+import 'package:flutter/material.dart';
+
+import 'app.dart';
+import 'core/config/app_config.dart';
+import 'core/di/injection_container.dart' as di;
+
+/// Production entry point.
+///
+/// Run with: flutter run -t lib/main_prod.dart --release
+/// Or with explicit env: flutter run --dart-define=ENV=prod
+/// Build APK: flutter build apk -t lib/main_prod.dart --release
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+
+  // Initialize production configuration
+  AppConfig.initialize(environment: 'prod');
+
+  // Initialize dependency injection
+  await di.init();
+
+  runApp(const AgendaApp());
+}