feat: add payment card grouping and analysis

lib/utils/payment_card_utils.dart

@@ -0,0 +1,41 @@
+import 'package:flutter/material.dart';
+
+/// 결제수단 관련 공통 유틸리티
+class PaymentCardUtils {
+  static const List<String> colorPalette = [
+    '#FF6B6B',
+    '#F97316',
+    '#F59E0B',
+    '#10B981',
+    '#06B6D4',
+    '#3B82F6',
+    '#6366F1',
+    '#8B5CF6',
+    '#EC4899',
+    '#14B8A6',
+    '#0EA5E9',
+    '#94A3B8',
+  ];
+
+  static const Map<String, IconData> iconMap = {
+    'credit_card': Icons.credit_card_rounded,
+    'payments': Icons.payments_rounded,
+    'wallet': Icons.account_balance_wallet_rounded,
+    'bank': Icons.account_balance_rounded,
+    'shopping': Icons.shopping_bag_rounded,
+    'subscriptions': Icons.subscriptions_rounded,
+    'bolt': Icons.bolt_rounded,
+  };
+
+  static IconData iconForName(String name) {
+    return iconMap[name] ?? Icons.credit_card_rounded;
+  }
+
+  static Color colorFromHex(String hex) {
+    var value = hex.replaceAll('#', '');
+    if (value.length == 6) {
+      value = 'ff$value';
+    }
+    return Color(int.parse(value, radix: 16));
+  }
+}