feat: add payment card grouping and analysis

lib/widgets/detail/detail_form_section.dart

@@ -9,6 +9,9 @@ import '../common/form_fields/date_picker_field.dart';
 import '../common/form_fields/currency_dropdown_field.dart';
 import '../common/form_fields/billing_cycle_selector.dart';
 import '../common/form_fields/category_selector.dart';
+import '../payment_card/payment_card_selector.dart';
+import '../payment_card/payment_card_form_sheet.dart';
+import '../../routes/app_routes.dart';
 import '../../l10n/app_localizations.dart';
 
 /// 상세 화면 폼 섹션
@@ -184,6 +187,33 @@ class DetailFormSection extends StatelessWidget {
                         );
                       },
                     ),
+                    const SizedBox(height: 20),
+                    Text(
+                      AppLocalizations.of(context).paymentCard,
+                      style: TextStyle(
+                        fontSize: 16,
+                        fontWeight: FontWeight.w600,
+                        color: Theme.of(context).colorScheme.onSurface,
+                      ),
+                    ),
+                    const SizedBox(height: 8),
+                    PaymentCardSelector(
+                      selectedCardId: controller.selectedPaymentCardId,
+                      onChanged: (cardId) {
+                        controller.selectedPaymentCardId = cardId;
+                      },
+                      onAddCard: () async {
+                        final newCardId =
+                            await PaymentCardFormSheet.show(context);
+                        if (newCardId != null) {
+                          controller.selectedPaymentCardId = newCardId;
+                        }
+                      },
+                      onManageCards: () {
+                        Navigator.of(context)
+                            .pushNamed(AppRoutes.paymentCardManagement);
+                      },
+                    ),
                   ],
                 ),
               ),