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/blocs/group/group_state.dart

@@ -1,6 +1,24 @@
+/// States for group-related operations in the GroupBloc.
+///
+/// This file defines all possible states that the GroupBloc can emit in response
+/// to group-related events. The states represent different phases of group
+/// operations including loading, success, error, and data states.
+///
+/// State Categories:
+/// - **Initial State**: GroupInitial
+/// - **Loading States**: GroupLoading
+/// - **Success States**: GroupsLoaded, GroupLoaded, GroupCreated, GroupOperationSuccess
+/// - **Error States**: GroupError
+///
+/// All states extend [GroupState] and implement [Equatable] for proper
+/// equality comparison and state change detection in the BLoC pattern.
 import 'package:equatable/equatable.dart';
 import '../../models/group.dart';
 
+/// Base class for all group-related states.
+///
+/// All group states must extend this class and implement the [props] getter
+/// for proper equality comparison in the BLoC pattern.
 abstract class GroupState extends Equatable {
   const GroupState();
 
@@ -8,54 +26,132 @@ abstract class GroupState extends Equatable {
   List<Object?> get props => [];
 }
 
-// État initial
+// Initial state
+/// The initial state of the GroupBloc before any operations are performed.
+///
+/// This is the default state when the bloc is first created and represents
+/// a clean slate with no group data loaded or operations in progress.
 class GroupInitial extends GroupState {}
 
-// Chargement
+// Loading
+/// State indicating that a group operation is currently in progress.
+///
+/// This state is emitted when the bloc is performing operations like
+/// loading groups, creating groups, or updating group information.
+/// UI components can use this state to show loading indicators.
 class GroupLoading extends GroupState {}
 
-// Groupes chargés
+// Groups loaded
+/// State containing a list of successfully loaded groups.
+///
+/// This state is emitted when groups have been successfully retrieved
+/// from the repository, either through initial loading or real-time updates.
+/// The UI can use this data to display the list of available groups.
+///
+/// Properties:
+///   [groups]: List of Group objects that were loaded
 class GroupsLoaded extends GroupState {
+  /// The list of loaded groups
   final List<Group> groups;
 
+  /// Creates a GroupsLoaded state.
+  ///
+  /// Args:
+  ///   [groups]: The list of groups to include in this state
   const GroupsLoaded(this.groups);
 
   @override
   List<Object?> get props => [groups];
 }
 
+/// Alternative state for loaded groups (used in some contexts).
+///
+/// This state serves a similar purpose to GroupsLoaded but may be used
+/// in different contexts or for backward compatibility.
+///
+/// Properties:
+///   [groups]: List of Group objects that were loaded
 class GroupLoaded extends GroupState {
+  /// The list of loaded groups
   final List<Group> groups;
 
+  /// Creates a GroupLoaded state.
+  ///
+  /// Args:
+  ///   [groups]: The list of groups to include in this state
   const GroupLoaded(this.groups);
 }
 
+/// State indicating successful group creation.
+///
+/// This state is emitted when a new group has been successfully created.
+/// It contains the ID of the newly created group and an optional success message
+/// that can be displayed to the user.
+///
+/// Properties:
+///   [groupId]: The unique identifier of the newly created group
+///   [message]: A success message to display to the user
 class GroupCreated extends GroupState {
+  /// The unique identifier of the newly created group
   final String groupId;
+  
+  /// Success message for the user
   final String message;
 
+  /// Creates a GroupCreated state.
+  ///
+  /// Args:
+  ///   [groupId]: The ID of the newly created group
+  ///   [message]: Optional success message (defaults to "Group created successfully")
   const GroupCreated({
     required this.groupId,
-    this.message = 'Groupe créé avec succès',
+    this.message = 'Group created successfully',
   });
+  
   @override
   List<Object?> get props => [groupId, message];
 }
 
-// Succès d'une opération
+// Operation success
+/// State indicating successful completion of a group operation.
+///
+/// This state is emitted when operations like updating, deleting, or
+/// member management have completed successfully. It contains a message
+/// that can be displayed to inform the user of the successful operation.
+///
+/// Properties:
+///   [message]: A success message describing the completed operation
 class GroupOperationSuccess extends GroupState {
+  /// The success message to display to the user
   final String message;
 
+  /// Creates a GroupOperationSuccess state.
+  ///
+  /// Args:
+  ///   [message]: The success message to display
   const GroupOperationSuccess(this.message);
 
   @override
   List<Object?> get props => [message];
 }
 
-// Erreur
+// Error
+/// State indicating that a group operation has failed.
+///
+/// This state is emitted when any group operation encounters an error.
+/// It contains an error message that can be displayed to the user to
+/// explain what went wrong.
+///
+/// Properties:
+///   [message]: An error message describing what went wrong
 class GroupError extends GroupState {
+  /// The error message to display to the user
   final String message;
 
+  /// Creates a GroupError state.
+  ///
+  /// Args:
+  ///   [message]: The error message to display
   const GroupError(this.message);
 
   @override