HerregistratieReminderJob (Quartz IJob) fires HerregistratieReminderSweep on a
daily cron wired in Big.Api (overridable via Quartz__Cron), and logs how many
reminders went out. Quartz.NET is used for this time-triggered fleet sweep,
distinct from the queue-draining pumps (ADR-0022). GET /registrations/{id} now
returns herregistratieVoor + herregistratieReminderVerstuurd. The scheduling
shell is excluded from mutation, mirroring the pumps.
refs #18