refactor: remove categoryName from TransactionRecord and use category reference

finance_app/lib/models/transaction_record.dart

@@ -4,7 +4,6 @@ import 'category.dart';
 class TransactionRecord {
   final int id;
   final String type; // 'income' or 'expense'
-  final String categoryName;
   final double amount;
   final Category? category; // Reference to category (null for income)
   final DateTime date;
@@ -13,9 +12,8 @@ class TransactionRecord {
   TransactionRecord({
     required this.id,
     required this.type,
-    required this.categoryName,
     required this.amount,
-    this.category, // Optional since income may not have a category
+    this.category,
     required this.date,
     required this.merchant,
   });

finance_app/lib/screens/expenses_screen.dart

@@ -499,14 +499,19 @@ class _ExpensesScreenState extends State<ExpensesScreen> with TickerProviderStat
 
                                       // Create the model.TransactionRecord needed by TransactionListItem
                                       final transactionRecord = model.TransactionRecord(
-                                        id: dbTransaction.id, // Pass the actual ID
-                                        type: dbTransaction.type, // Pass the type
-                                        categoryName: dbTransaction.categoryName, // Pass category or 'Income'
+                                        id: dbTransaction.id,
+                                        type: dbTransaction.type,
                                         amount: dbTransaction.amount,
-                                        iconCode: categoryDetails.iconCode, // Get icon
-                                        color: categoryDetails.colorCode, // Get color
+                                        category: dbTransaction.type == 'expense' 
+                                          ? Category(
+                                              dbTransaction.categoryName,
+                                              dbTransaction.amount,
+                                              categoryDetails.colorCode,
+                                              categoryDetails.iconCode,
+                                            )
+                                          : null,
                                         date: dbTransaction.date,
-                                        merchant: dbTransaction.merchant, // Pass merchant or source
+                                        merchant: dbTransaction.merchant,
                                       );
 
                                       // Use the TransactionListItem widget

finance_app/lib/widgets/transaction_list_item.dart

@@ -81,7 +81,7 @@ class TransactionListItem extends StatelessWidget {
 
         // Title: Category Name (for expense) or "Income"
         title: Text(
-          isIncome ? 'Income' : transaction.categoryName, // Show "Income" or category name
+          isIncome ? 'Income' : transaction.category?.name ?? 'Uncategorized', // Show "Income" or category name
           style: const TextStyle(
             fontWeight: FontWeight.w600,
             fontSize: 14.5,