feat: add payment card grouping and analysis

lib/models/subscription.dart

@@ -1,3 +1,5 @@
+import 'payment_card_suggestion.dart';
+
 class Subscription {
   final String id;
   final String serviceName;
@@ -10,6 +12,8 @@ class Subscription {
   final DateTime? lastPaymentDate;
   final String? websiteUrl;
   final String currency;
+  final String? paymentCardId;
+  final PaymentCardSuggestion? paymentCardSuggestion;
 
   Subscription({
     required this.id,
@@ -23,6 +27,8 @@ class Subscription {
     this.lastPaymentDate,
     this.websiteUrl,
     this.currency = 'KRW',
+    this.paymentCardId,
+    this.paymentCardSuggestion,
   });
 
   Map<String, dynamic> toMap() {
@@ -38,6 +44,10 @@ class Subscription {
       'lastPaymentDate': lastPaymentDate?.toIso8601String(),
       'websiteUrl': websiteUrl,
       'currency': currency,
+      'paymentCardId': paymentCardId,
+      'paymentCardSuggestionIssuer': paymentCardSuggestion?.issuerName,
+      'paymentCardSuggestionLast4': paymentCardSuggestion?.last4,
+      'paymentCardSuggestionSource': paymentCardSuggestion?.source,
     };
   }
 
@@ -56,6 +66,14 @@ class Subscription {
           : null,
       websiteUrl: map['websiteUrl'] as String?,
       currency: map['currency'] as String? ?? 'KRW',
+      paymentCardId: map['paymentCardId'] as String?,
+      paymentCardSuggestion: map['paymentCardSuggestionIssuer'] != null
+          ? PaymentCardSuggestion(
+              issuerName: map['paymentCardSuggestionIssuer'] as String,
+              last4: map['paymentCardSuggestionLast4'] as String?,
+              source: map['paymentCardSuggestionSource'] as String?,
+            )
+          : null,
     );
   }