Refactor useBudgetState into smaller files

Refactors the `useBudgetState.ts` file into smaller, more manageable files to improve code organization and maintainability. No functionality is changed.

src/contexts/budget/hooks/useCategorySpending.ts

@@ -0,0 +1,17 @@
+
+import { useCallback } from 'react';
+import { Transaction } from '../types';
+import { calculateCategorySpending } from '../budgetUtils';
+
+// 카테고리별 지출 계산 훅
+export const useCategorySpending = (
+  transactions: Transaction[], 
+  categoryBudgets: Record<string, number>
+) => {
+  // 카테고리별 지출 계산
+  const getCategorySpending = useCallback(() => {
+    return calculateCategorySpending(transactions, categoryBudgets);
+  }, [transactions, categoryBudgets]);
+
+  return { getCategorySpending };
+};