Wires the billingEntityType/billingEntityId columns (added in PR 1) through
the invoice validator and service. Clients can now be billed as either a
client or a company; clientName becomes a snapshot derived from the entity
at create time.
- createInvoiceSchema: replace clientName with billingEntity {type,id}
- listInvoicesSchema: add billingEntityType/billingEntityId filters
- createInvoice: resolveBillingEntity helper (tenant-scoped; tx-aware)
falls back to entity primary email/address when not supplied
- listInvoices: honor new billing-entity filters
- updateInvoice: unchanged — billing entity is fixed after create
- invoice wizard step 1: temporary billing-entity id input (Task 10.2
replaces this with a proper picker)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
