Finalize and email one held invoice immediately, recording who and why.

Brings the send forward; it does not authorise one. The daily pass would send the same invoice on its next run, which for a send date already behind us means tomorrow morning — this is for the operator who is looking at it now. Irreversible — a finalized invoice cannot be returned to draft — so the caller is expected to have confirmed it with the operator, and reason is required.

sent=false covers three different endings, and only the returned invoice.state separates them: still ready means a guard held it — an S3 credit is not yet on Stripe — and the daily pass retries; void means Stripe has voided or written off the invoice, so the review row is retired and nothing retries; sent means it had already gone. A caller that reads sent alone will tell the operator the wrong thing in two cases out of three.