feat: add payment card grouping and analysis

lib/widgets/subscription_card.dart

@@ -2,10 +2,12 @@ import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import '../models/subscription_model.dart';
 import '../providers/category_provider.dart';
+import '../providers/payment_card_provider.dart';
 import '../providers/locale_provider.dart';
 import '../services/subscription_url_matcher.dart';
 import '../services/currency_util.dart';
 import '../utils/billing_date_util.dart';
+import '../utils/payment_card_utils.dart';
 import 'website_icon.dart';
 import 'app_navigator.dart';
 // import '../theme/app_colors.dart';
@@ -299,6 +301,7 @@ class _SubscriptionCardState extends State<SubscriptionCard>
   Widget build(BuildContext context) {
     // LocaleProvider를 watch하여 언어 변경시 자동 업데이트
     final localeProvider = context.watch<LocaleProvider>();
+    final paymentCardProvider = context.watch<PaymentCardProvider>();
 
     // 언어가 변경되면 displayName 다시 로드
     WidgetsBinding.instance.addPostFrameCallback((_) {
@@ -464,7 +467,10 @@ class _SubscriptionCardState extends State<SubscriptionCard>
                               ],
                             ),
 
-                            const SizedBox(height: 6),
+                            const SizedBox(height: 8),
+                            _buildPaymentCardBadge(
+                                context, paymentCardProvider),
+                            const SizedBox(height: 8),
 
                             // 가격 정보
                             Row(
@@ -673,4 +679,57 @@ class _SubscriptionCardState extends State<SubscriptionCard>
       ),
     );
   }
+
+  Widget _buildPaymentCardBadge(
+      BuildContext context, PaymentCardProvider provider) {
+    final scheme = Theme.of(context).colorScheme;
+    final loc = AppLocalizations.of(context);
+    final card = provider.getCardById(widget.subscription.paymentCardId);
+
+    if (card == null) {
+      return Chip(
+        avatar: Icon(
+          Icons.credit_card_off_rounded,
+          size: 14,
+          color: scheme.onSurfaceVariant,
+        ),
+        label: Text(
+          loc.paymentCardUnassigned,
+          style: TextStyle(
+            fontSize: 12,
+            color: scheme.onSurfaceVariant,
+          ),
+        ),
+        backgroundColor: scheme.surfaceContainerHighest.withValues(alpha: 0.5),
+        padding: const EdgeInsets.symmetric(horizontal: 6),
+        materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
+      );
+    }
+
+    final color = PaymentCardUtils.colorFromHex(card.colorHex);
+    final icon = PaymentCardUtils.iconForName(card.iconName);
+
+    return Chip(
+      avatar: CircleAvatar(
+        backgroundColor: Colors.white,
+        child: Icon(
+          icon,
+          size: 14,
+          color: color,
+        ),
+      ),
+      label: Text(
+        '${card.issuerName} · ****${card.last4}',
+        style: TextStyle(
+          fontSize: 12,
+          fontWeight: FontWeight.w600,
+          color: color,
+        ),
+      ),
+      side: BorderSide(color: color.withValues(alpha: 0.3)),
+      backgroundColor: color.withValues(alpha: 0.12),
+      padding: const EdgeInsets.symmetric(horizontal: 8),
+      materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
+    );
+  }
 }