체험 계정도 업그레이드 승인되도록 수정

lib/upgrade-requests.ts

@@ -148,10 +148,20 @@ export async function approveUpgradeRequest(
     });
 
     // Re-verify upgrade direction at approval time (maestro AccountType may have changed since request)
+    const isRequestedPaid = (PAID_ACCOUNT_TYPE_VALUES as readonly number[]).includes(
+      request!.RequestedAccountType
+    );
+    const isCurrentPaid = (PAID_ACCOUNT_TYPE_VALUES as readonly number[]).includes(
+      request!.maestro.AccountType
+    );
     const isApprovalTrial = request!.maestro.ActivateStatus === ACTIVATE_STATUSES.TRIAL;
-    const isStillValidUpgrade = isApprovalTrial
-      ? request!.RequestedAccountType >= request!.maestro.AccountType
-      : request!.RequestedAccountType > request!.maestro.AccountType;
+    const isStillValidUpgrade =
+      isRequestedPaid &&
+      (!isCurrentPaid
+        ? true
+        : isApprovalTrial
+          ? request!.RequestedAccountType >= request!.maestro.AccountType
+          : request!.RequestedAccountType > request!.maestro.AccountType);
     if (!isStillValidUpgrade) {
       throw new ApiError(
         "마에스트로의 현재 요금제 기준으로 유효하지 않은 업그레이드입니다. 신청 내용을 확인해 주세요.",
@@ -214,10 +224,22 @@ export async function createUpgradeRequest(
       throw new ApiError("마에스트로를 찾을 수 없습니다.", 404);
     }
 
+    const isRequestedPaid = (PAID_ACCOUNT_TYPE_VALUES as readonly number[]).includes(
+      requestedAccountType
+    );
+    if (!isRequestedPaid) {
+      throw new ApiError("업그레이드 대상은 유료 요금제여야 합니다.", 400);
+    }
+
+    const isCurrentPaid = (PAID_ACCOUNT_TYPE_VALUES as readonly number[]).includes(
+      maestro.AccountType
+    );
     const isTrial = maestro.ActivateStatus === ACTIVATE_STATUSES.TRIAL;
-    const isValidUpgrade = isTrial
-      ? requestedAccountType >= maestro.AccountType
-      : requestedAccountType > maestro.AccountType;
+    const isValidUpgrade = !isCurrentPaid
+      ? true
+      : isTrial
+        ? requestedAccountType >= maestro.AccountType
+        : requestedAccountType > maestro.AccountType;
 
     if (!isValidUpgrade) {
       throw new ApiError(