Groups all invoices matching the given filter by invoice_status and returns counts/totals per status. Always zero-fills all 9 statuses (DRAFT, READY_TO_INVOICE, AWAIT_PAYMENT, PARTIALLY_PAID, PAID, BAD_DEBT, ARCHIVED, CLOSED, CANCELED) even when empty — unlike the analogous Estimate endpoint, no status is ever filtered out. Amounts rounded to the company's decimal_roundoff config.