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/components/expenses/ExpenseForm.tsx

@@ -8,11 +8,14 @@ import { Loader2 } from 'lucide-react';
 import ExpenseCategorySelector from './ExpenseCategorySelector';
 import { Badge } from '@/components/ui/badge';
 import { getPersonalizedTitleSuggestions } from '@/utils/userTitlePreferences';
+import { Separator } from '@/components/ui/separator';
+import { RadioGroup, RadioGroupItem } from '@/components/ui/radio-group';
 
 export interface ExpenseFormValues {
   title: string;
   amount: string;
   category: string;
+  paymentMethod: '신용카드' | '현금';
 }
 
 interface ExpenseFormProps {
@@ -27,6 +30,7 @@ const ExpenseForm: React.FC<ExpenseFormProps> = ({ onSubmit, onCancel, isSubmitt
       title: '',
       amount: '',
       category: '음식',
+      paymentMethod: '신용카드'
     }
   });
   
@@ -113,7 +117,7 @@ const ExpenseForm: React.FC<ExpenseFormProps> = ({ onSubmit, onCancel, isSubmitt
           )}
         />
         
-        {/* 금액 필드를 마지막으로 배치 */}
+        {/* 금액 필드를 세 번째로 배치 */}
         <FormField
           control={form.control}
           name="amount"
@@ -130,6 +134,36 @@ const ExpenseForm: React.FC<ExpenseFormProps> = ({ onSubmit, onCancel, isSubmitt
           )}
         />
         
+        {/* 구분선 추가 */}
+        <Separator className="my-2" />
+        
+        {/* 지출 방법 필드 추가 */}
+        <FormField
+          control={form.control}
+          name="paymentMethod"
+          render={({ field }) => (
+            <FormItem>
+              <FormLabel>지출 방법</FormLabel>
+              <RadioGroup
+                onValueChange={field.onChange}
+                defaultValue={field.value}
+                className="flex gap-4"
+                value={field.value}
+                disabled={isSubmitting}
+              >
+                <div className="flex items-center space-x-2">
+                  <RadioGroupItem value="신용카드" id="credit-card" />
+                  <label htmlFor="credit-card" className="cursor-pointer">신용카드</label>
+                </div>
+                <div className="flex items-center space-x-2">
+                  <RadioGroupItem value="현금" id="cash" />
+                  <label htmlFor="cash" className="cursor-pointer">현금</label>
+                </div>
+              </RadioGroup>
+            </FormItem>
+          )}
+        />
+        
         <div className="flex justify-end gap-2 pt-2">
           <Button 
             type="button"