Return a valid Turbo frame when poll completion is rejected

In meeting 11 Chrome acceptance, clicking enabled “Fullfør votering” on an active bias poll before any votes were recorded returned HTTP 200 without the expected turbo-frame id poll_buttons_case_9. Turbo replaced the controls with “Content missing” and logged that the response lacked the expected frame; the poll correctly remained ongoing and was recoverable only by recording votes. Rejected/non-completable poll actions must return the expected poll-buttons frame plus a visible validation message, without destroying the active controls. Check ordinary and bias poll completion paths.