Adds a drag-and-drop/click upload field on the invoice editor for an
optional 420x210 JPG/PNG signature image. The signature is stored as
part of invoice_data and rendered on the generated PDF directly above
the QR code, right-aligned with sensible margins.
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
The create-screen "print" action used a separate browser-rendered HTML
template while ZIP exports used a PDFKit-rendered PDF, so the two looked
different. Extract the ZIP export's PDF rendering into a shared
renderInvoicePdf function, add a POST /api/invoices/pdf endpoint that
renders the current editor form data through it, and have the print
button download that PDF instead of opening a print window with the old
HTML template.
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
