Add payment method selection

Adds a payment method selection (Credit Card, Cash) to the expense form and includes a line separator. Also requests to add a graph showing the proportion of credit card and cash usage in expense analytics, but this part is not implemented in this commit.

src/contexts/budget/types.ts

@@ -30,6 +30,7 @@ export interface BudgetContextType {
   updateTransaction: (updatedTransaction: Transaction) => void;
   handleBudgetGoalUpdate: (type: BudgetPeriod, amount: number, newCategoryBudgets?: Record<string, number>) => void;
   getCategorySpending: () => CategoryBudget[];
+  getPaymentMethodStats: () => { method: string; amount: number; percentage: number }[];
 }
 
 // Transaction 타입 (기존 TransactionCard에서 가져옴)
@@ -40,6 +41,7 @@ export interface Transaction {
   date: string;
   category: string;
   type: 'income' | 'expense';
+  paymentMethod?: '신용카드' | '현금'; // 지출 방법 추가
   notes?: string;
   localTimestamp?: string; // 로컬 수정 타임스탬프 추가
   serverTimestamp?: string; // 서버 타임스탬프 추가