The fix in v3.15.8 made scheduleConfig.autoMirror an independent trigger
in the scheduler, but it remained reachable only via the AUTO_MIRROR_REPOS
env var. This adds a UI checkbox under the Automatic Syncing section so
the option can be toggled per-config without touching the environment.
The toggle is conditional on scheduling being enabled (since auto-mirror
without a scheduler is meaningless) and is independent of the existing
"Auto-mirror new starred repositories" toggle in GitHub settings. Together
they cover the full owned/starred matrix that the scheduler already
supports.
Plumbing: config-mapper.ts now round-trips autoMirror through the UI/DB
boundary, and ScheduleConfig in types/config.ts gets the matching field.
No schema or migration change — autoMirror was already in the zod schema.
