// Body
{ "name": "T-Shirt Print Calculator", "status": "draft" }

// Response 201
{
  "id":        "clx1234abcd",
  "shop":      "myshop.myshopify.com",
  "name":      "T-Shirt Print Calculator",
  "status":    "draft",
  "createdAt": "2026-04-30T10:00:00Z"
}

// Body
{
  "expression": "quantity * price_per_unit + setup_fee",
  "testValues": { "quantity": 100, "price_per_unit": 2.5, "setup_fee": 25 }
}

// Response 200
{ "result": 275, "valid": true }

// Form fields
shop           = "myshop.myshopify.com"
calculator_id  = "clx1234abcd"
customer_email = "john@example.com"
values         = '{"quantity":100,"material":"cotton"}'
final_price    = "275"
file_upload_0  = [Binary File]

// Response 200
{ "success": true, "reference": "QF-1746000000" }