Recommend Presigned Uploads for Application Form Submit

The Creating a Custom Careers Page guide now recommends the presigned flow. Inlining file bytes in a multipart request remains supported but is slower and less reliable. applicationForm.submit submissions with file fields should use a handle from file.createFileUploadHandle in a JSON body.
The guide now describes the applicationForm.submit success response correctly: recorded responses come back in a submittedValues object keyed by field path, not an array.