Generate PDF preview (no DB write)

curl --location '/api/v1/core/documents/preview' \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data-raw '{
    "delivery": {
        "companyCode": "GO51104",
        "companyBranchCode": "00000",
        "email": "buyer@example.com"
    },
    "header": {
        "documentType": "388",
        "templateNo": "INV-7QX2K9",
        "issueDate": "2026-06-17T10:30:00+07:00",
        "isVatIncluded": false,
        "buyer": {
            "name": "บริษัท ตัวอย่าง จำกัด",
            "taxId": "0105556000000",
            "taxIdSchemeId": "TXID",
            "branchNo": "00000",
            "buildingNumber": "123",
            "street": "สุขุมวิท",
            "subDistrictCode": "100502",
            "districtCode": "1005",
            "provinceCode": "10",
            "postCode": "10110",
            "countryCode": "TH"
        }
    },
    "items": [
        {
            "lineId": 1,
            "productName": "บริการที่ปรึกษา",
            "unitPrice": 1000,
            "quantity": 2,
            "unit": "ครั้ง",
            "vatTypeCode": "VAT"
        }
    ],
    "remark": "ชำระภายใน 30 วัน"
}'