Implements the split decided in review:
Incoming invoices (external) - the inbound_documents row IS the payable:
- categorizeInbound now UPDATES the document (disposition + tax_treatment +
booking event_id (null=company) + category), no derived expense row, so a
supplier invoice appears only in the incoming-invoices surface.
- rebillInbound mints the client invoice from the document (base = invoice
total + markup) and links it on the doc.
- markInboundSupplierPayment records supplier payment ON the incoming invoice
(mark-paid lives here now).
Expenses (internal) - own costs only:
- createExpense: kind = amount|mileage|per_diem; amount = quantity x rate
(rate from accounting settings, per-entry override; snapshotted); optional
proof file; booked to an event or the company; require-proof enforced from
settings. No supplier payment, always own-cost.
- listExpenses returns internal rows only (inbound_document_id IS NULL).
Routes: per-flag gating (incomingInvoices vs expenses; categories on the
accounting master); supplier-payment + re-bill moved under /inbound/:id/*;
POST/PATCH expenses accept a multipart proof upload; GET /:id/proof streams it
(PDF download-only, image inline). getAccountingSettings reads app_settings.
Verified: node -c, require-graph, 12 unit tests (markup + expense amount/build).
Frontend rework (service + the two UIs + settings tab + category i18n) follows.