Get Invoice Provenance

master spec §3.9: 'production-to-billing parcel provenance in the invoice evidence drawer' — 'per-piece invoices show which parcels/ batches rolled into the period.' Only a term line with pricing_model 'per_parcel' (renamed from 'per_piece' by migrations/ 0077_contract_terms.sql) has a per-piece provenance story; a per_adp/ flat (or term-less manual) invoice gets an honest applicable: false instead of a fabricated parcel list. Calls app.modules.fulfillment.service directly (module-to-module composition, the same cross-module pattern app/modules/print/service.py already uses against Fulfillment) rather than duplicating a parcels query here.