Enhance model and service documentation with detailed comments and descriptions

- Updated Group, Trip, User, and other model classes to include comprehensive documentation for better understanding and maintainability.
- Improved error handling and logging in services, including AuthService, ErrorService, and StorageService.
- Added validation and business logic explanations in ExpenseService and TripService.
- Refactored method comments to follow a consistent format across the codebase.
- Translated error messages and comments from French to English for consistency.

lib/pages/login.dart

@@ -4,7 +4,13 @@ import '../blocs/auth/auth_bloc.dart';
 import '../blocs/auth/auth_event.dart';
 import '../blocs/auth/auth_state.dart';
 
+/// Login page widget for user authentication.
+/// 
+/// This page provides a user interface for signing in with email and password,
+/// as well as options for social sign-in (Google, Apple) and password reset.
+/// It integrates with the AuthBloc to handle authentication state management.
 class LoginPage extends StatefulWidget {
+  /// Creates a new [LoginPage].
   const LoginPage({super.key});
 
   @override
@@ -12,9 +18,16 @@ class LoginPage extends StatefulWidget {
 }
 
 class _LoginPageState extends State<LoginPage> {
+  /// Form key for validation
   final _formKey = GlobalKey<FormState>();
+  
+  /// Controller for email input field
   final _emailController = TextEditingController();
+  
+  /// Controller for password input field
   final _passwordController = TextEditingController();
+  
+  /// Whether the password field should hide its content
   bool _obscurePassword = true;
 
   @override
@@ -24,24 +37,36 @@ class _LoginPageState extends State<LoginPage> {
     super.dispose();
   }
 
+  /// Validates email input.
+  /// 
+  /// Returns an error message if the email is invalid or empty,
+  /// null if the email is valid.
   String? _validateEmail(String? value) {
     if (value == null || value.trim().isEmpty) {
-      return 'Email requis';
+      return 'Email required';
     }
     final emailRegex = RegExp(r'^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$');
     if (!emailRegex.hasMatch(value.trim())) {
-      return 'Email invalide';
+      return 'Invalid email';
     }
     return null;
   }
 
+  /// Validates password input.
+  /// 
+  /// Returns an error message if the password is empty,
+  /// null if the password is valid.
   String? _validatePassword(String? value) {
     if (value == null || value.isEmpty) {
-      return 'Mot de passe requis';
+      return 'Password required';
     }
     return null;
   }
 
+  /// Handles the login process.
+  /// 
+  /// Validates the form and dispatches a sign-in event to the AuthBloc
+  /// if all fields are valid.
   void _login(BuildContext context) {
     if (!_formKey.currentState!.validate()) {
       return;