Adds a payment step after document approval: PM_Freigabe approves
(Field 15 = "freigegeben"), then PM_Zahlung can mark as paid (Field 16).
- Backend: VIEW_ZAHLUNG permission mapped to PM_Zahlung OIDC group
- Backend: ZahlungModule with endpoints to list documents by filter
(ausstehend/freigegeben/alle), set Field 16, fetch options from Paperless
- Backend: setZahlung() throws ForbiddenException if Field 15 ≠ "freigegeben"
- Frontend: /zahlung route with 3-way filter, two status columns (Freigabe + Zahlung)
- Frontend: "Zahlung verbuchen" button disabled with tooltip for non-approved docs
- Frontend: Zahlung menu item with EuroOutlined icon
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
