feat(error): add PermissionDenied error code

- Add error code 40008 for permission denied scenarios
- Add corresponding error message for admin permission checks

pkg/xerr/errCode.go

@@ -50,6 +50,7 @@ const (
 	InvalidAccess     uint32 = 40005
 	InvalidCiphertext uint32 = 40006
 	SecretIsEmpty     uint32 = 40007
+	PermissionDenied  uint32 = 40008
 )
 
 //coupon error

pkg/xerr/errMsg.go

@@ -17,6 +17,7 @@ func init() {
 		SecretIsEmpty:     "Secret is empty",
 		InvalidAccess:     "Invalid access",
 		InvalidCiphertext: "Invalid ciphertext",
+		PermissionDenied:  "Permission denied",
 		// Database error
 		DatabaseQueryError:   "Database query error",
 		DatabaseUpdateError:  "Database update error",