Restore debate controls when a poll is cancelled

Chrome lifecycle testing in meeting 13 showed that starting an ordinary poll changes debate controls from “Sett strek” / “Steng replikker” to “Strek satt” / “Replikker stengt”. After “Avbryt votering”, these locked states persist immediately and after hard refresh even though the proposal is startable again. Poll cancellation should restore proposal/point and associated debate-control state to the pre-poll lifecycle state atomically, or clearly preserve it only if that is intended policy. Add cancellation and refresh regression coverage.