feat: Add User and UserBalance models with serialization methods

feat: Implement BalanceRepository for group balance calculations

feat: Create ExpenseRepository for managing expenses

feat: Add services for handling expenses and storage operations

fix: Update import paths for models in repositories and services

refactor: Rename CountContent to AccountContent in HomePage

chore: Add StorageService for image upload and management

lib/repositories/expense_repository.dart

@@ -0,0 +1,113 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+import '../models/expense.dart';
+import '../services/error_service.dart';
+
+class ExpenseRepository {
+  final FirebaseFirestore _firestore;
+  final ErrorService _errorService;
+
+  ExpenseRepository({
+    FirebaseFirestore? firestore,
+    ErrorService? errorService,
+  }) : _firestore = firestore ?? FirebaseFirestore.instance,
+       _errorService = errorService ?? ErrorService();
+
+  CollectionReference get _expensesCollection => _firestore.collection('expenses');
+
+  // Stream des dépenses d'un groupe
+  Stream<List<Expense>> getExpensesStream(String groupId) {
+    return _expensesCollection
+        .where('groupId', isEqualTo: groupId)
+        .where('isArchived', isEqualTo: false)
+        .orderBy('createdAt', descending: true)
+        .snapshots()
+        .map((snapshot) {
+      return snapshot.docs
+          .map((doc) => Expense.fromMap(doc.data() as Map<String, dynamic>, doc.id))
+          .toList();
+    }).handleError((error) {
+      _errorService.logError('ExpenseRepository', 'Erreur stream expenses: $error');
+      return <Expense>[];
+    });
+  }
+
+  // Créer une dépense
+  Future<String> createExpense(Expense expense) async {
+    try {
+      final docRef = await _expensesCollection.add(expense.toMap());
+      return docRef.id;
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur création expense: $e');
+      rethrow;
+    }
+  }
+
+  // Mettre à jour une dépense
+  Future<void> updateExpense(Expense expense) async {
+    try {
+      final updateData = expense.toMap();
+      updateData['editedAt'] = FieldValue.serverTimestamp();
+      updateData['isEdited'] = true;
+      
+      await _expensesCollection.doc(expense.id).update(updateData);
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur update expense: $e');
+      rethrow;
+    }
+  }
+
+  // Supprimer une dépense
+  Future<void> deleteExpense(String expenseId) async {
+    try {
+      await _expensesCollection.doc(expenseId).delete();
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur delete expense: $e');
+      rethrow;
+    }
+  }
+
+  // Marquer un split comme payé
+  Future<void> markSplitAsPaid(String expenseId, String userId) async {
+    try {
+      await _firestore.runTransaction((transaction) async {
+        final expenseDoc = await transaction.get(_expensesCollection.doc(expenseId));
+        
+        if (!expenseDoc.exists) {
+          throw Exception('Dépense non trouvée');
+        }
+
+        final expense = Expense.fromMap(
+          expenseDoc.data() as Map<String, dynamic>, 
+          expenseDoc.id
+        );
+
+        final updatedSplits = expense.splits.map((split) {
+          if (split.userId == userId) {
+            return split.copyWith(isPaid: true, paidAt: DateTime.now());
+          }
+          return split;
+        }).toList();
+
+        transaction.update(expenseDoc.reference, {
+          'splits': updatedSplits.map((s) => s.toMap()).toList(),
+        });
+      });
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur mark split paid: $e');
+      rethrow;
+    }
+  }
+
+  // Archiver une dépense
+  Future<void> archiveExpense(String expenseId) async {
+    try {
+      await _expensesCollection.doc(expenseId).update({
+        'isArchived': true,
+        'archivedAt': FieldValue.serverTimestamp(),
+      });
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur archive expense: $e');
+      rethrow;
+    }
+  }
+}