Expose backend cron self-continuity (context_from=["self"]) in the Cron
editor. Adds a Run Continuity checkbox to the job editor that sends
context_from=["self"] on create and update (null when off, clearing it),
prefills from the loaded job's context_from, and shows a "Continuity" badge
on recurring jobs in the list. context_from was already on CronJob and
CreateCronJobRequest, so this is editor/list wiring only. Strings added for
en/zh/ko. Includes two ViewModel tests.
Co-authored-by: M57 <hy4ri@users.noreply.github.com>
