Aggregate applied bank-match coverage for a bill

DARK — 404s unless company_subledger_flags.ar_ap_items_enabled is true. Server-authoritative evidence the record-paid control gates on: coveredCents is the SUM of every applied document_match allocation against this bill's linked document, counted once per transaction, so a bill settled by several partial payments reports fullyCovered: true. Fails closed to zero coverage when the bill has no linked document. Deliberately served here rather than from the documents match-proposal read, which is gated by the unrelated intelligence-home flag.