fix(admin-app): fix 4 compile errors

- credit_page.dart: remove const from Padding containing context.t() call
- issuer_coupon_service/redemption_service/issuer_finance_service:
  cast inner['total'] to int? to match named record return type

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/admin-app/lib/core/services/issuer_coupon_service.dart

@@ -30,7 +30,7 @@ class IssuerCouponService {
               ?.map((e) => IssuerCouponModel.fromJson(e as Map<String, dynamic>))
               .toList() ??
           [];
-      return (items: items, total: inner['total'] ?? items.length);
+      return (items: items, total: (inner['total'] as int?) ?? items.length);
     } catch (e) {
       debugPrint('[IssuerCouponService] list 失败: $e');
       rethrow;

frontend/admin-app/lib/core/services/issuer_finance_service.dart

@@ -54,7 +54,7 @@ class IssuerFinanceService {
               ?.map((e) => TransactionModel.fromJson(e as Map<String, dynamic>))
               .toList() ??
           [];
-      return (items: items, total: inner['total'] ?? items.length);
+      return (items: items, total: (inner['total'] as int?) ?? items.length);
     } catch (e) {
       debugPrint('[IssuerFinanceService] getTransactions 失败: $e');
       rethrow;

frontend/admin-app/lib/core/services/redemption_service.dart

@@ -75,7 +75,7 @@ class RedemptionService {
               ?.map((e) => RedemptionRecord.fromJson(e as Map<String, dynamic>))
               .toList() ??
           [];
-      return (items: items, total: inner['total'] ?? items.length);
+      return (items: items, total: (inner['total'] as int?) ?? items.length);
     } catch (e) {
       debugPrint('[RedemptionService] getHistory 失败: $e');
       rethrow;

frontend/admin-app/lib/features/credit/presentation/pages/credit_page.dart

@@ -191,8 +191,8 @@ class _CreditPageState extends State<CreditPage> {
             );
           }),
           if (factors.isEmpty)
-            const Padding(
-              padding: EdgeInsets.all(16),
+            Padding(
+              padding: const EdgeInsets.all(16),
               child: Center(child: Text(context.t('credit_no_factors'), style: const TextStyle(color: AppColors.textTertiary))),
             ),
         ],