test: fix proxy repo stub

backend/internal/server/api_contract_test.go

@@ -858,6 +858,10 @@ func (stubProxyRepo) CountAccountsByProxyID(ctx context.Context, proxyID int64)
 	return 0, errors.New("not implemented")
 }
 
+func (stubProxyRepo) ListAccountSummariesByProxyID(ctx context.Context, proxyID int64) ([]service.ProxyAccountSummary, error) {
+	return nil, errors.New("not implemented")
+}
+
 type stubRedeemCodeRepo struct{}
 
 func (stubRedeemCodeRepo) Create(ctx context.Context, code *service.RedeemCode) error {