[BUGFIX] Backend PDF generation fails - Migrate DocumentController to cart-pdf v13 API (FileWriterService)

[johfeu]

Current Behavior
The Backend Order DocumentController's generatePdfDocument() method uses the deprecated PdfService::createPdf() API which no longer exists in cart-pdf v13 see extcode/cart_pdf#35
When attempting to generate PDF documents (invoice, delivery note, etc.) from the backend order module, the following error occurs:

Call to undefined method Extcode\CartPdf\Service\PdfService::createPdf()

Additionally, the class_exists() check uses PdfService::class which always returns true even though the createPdf() method was removed in cart-pdf v13.

Expected behavior/output

• Backend PDF generation should work with cart-pdf v13
• Clicking "Generate Invoice/Delivery Note" in the backend order module should successfully create and attach the PDF to the order item
• The code should use the new cart-pdf v13 API: DocumentRenderService::renderDocument() + FileWriterService::writeContentToFile()

Use the same migration pattern is used in cart-pdf's own EventListener\Order\Finish\DocumentRenderer

Environment

• TYPO3 version(s): 13.4
• cart version: 11.7.1
• cart-pdf version: dev-main (v13 compatible)

[johfeu]

cart-documentcontroller-fix.patch