fix logger and redeem admin review findings

backend/internal/handler/admin/redeem_handler.go

@@ -249,16 +249,13 @@ func (h *RedeemHandler) BatchDelete(c *gin.Context) {
 		return
 	}
 
-	deleted, err := h.adminService.BatchDeleteRedeemCodes(c.Request.Context(), req.IDs)
+	result, err := h.adminService.BatchDeleteRedeemCodes(c.Request.Context(), req.IDs)
 	if err != nil {
 		response.ErrorFrom(c, err)
 		return
 	}
 
-	response.Success(c, gin.H{
-		"deleted": deleted,
-		"message": "Redeem codes deleted successfully",
-	})
+	response.Success(c, result)
 }
 
 // Expire handles expiring a redeem code