Refactor: Split useTransactions hook

Splits the `useTransactions` hook into smaller, more manageable files for improved code organization and maintainability. No functional changes are included.

src/utils/transactionUtils.ts

@@ -0,0 +1,31 @@
+
+import { Transaction } from '@/components/TransactionCard';
+
+// 월별로 트랜잭션 필터링
+export const filterTransactionsByMonth = (
+  transactions: Transaction[], 
+  selectedMonth: string
+): Transaction[] => {
+  return transactions.filter(transaction => 
+    transaction.date.includes(selectedMonth) && transaction.type === 'expense'
+  );
+};
+
+// 검색어로 트랜잭션 필터링
+export const filterTransactionsByQuery = (
+  transactions: Transaction[],
+  searchQuery: string
+): Transaction[] => {
+  if (!searchQuery.trim()) return transactions;
+  
+  const query = searchQuery.toLowerCase().trim();
+  return transactions.filter(transaction => 
+    transaction.title.toLowerCase().includes(query) || 
+    transaction.category.toLowerCase().includes(query)
+  );
+};
+
+// 총 지출 금액 계산
+export const calculateTotalExpenses = (transactions: Transaction[]): number => {
+  return transactions.reduce((sum, t) => sum + t.amount, 0);
+};