Enhance job removal logic and scheduler handling

- Updated the `safeRemoveBullJob` function to handle jobs belonging to a Job Scheduler, ensuring they are removed via `removeJobScheduler` instead of direct removal.
- Introduced `removeScheduleJobSchedulers` to streamline the removal of job schedulers associated with scheduled jobs.
- Improved error handling and logging for job removal operations, particularly for legacy and repeatable jobs.
- Refactored related functions in both the bot and WebUI to ensure consistent handling of job scheduling and removal across the application.

docs/PHASE-TRACKING.md

@@ -607,11 +607,13 @@
 - Dashboard: Timing-Mode (einmalig vs. Cron), naive `datetime-local` an Server, Fehlertexte i18n
 - Dark Mode: `color-scheme` + Input `text-foreground` für datetime-local Lesbarkeit
 - Shared Helper `resolveScheduleRunAt` / `guildLocalDateTimeToUtc`
+- Delete: Scheduler-Kinder (`repeat:…`) nicht per `job.remove()`; Legacy-Hash-IDs via `removeJobScheduler` / Scan
 
 ### Manuell testen
 
 - [ ] WebUI einmalig: Datum/Uhrzeit in Server-Zeitzone → Nachricht zur erwarteten lokalen Zeit
 - [ ] WebUI Cron `0 9 * * *` bei Europe/Berlin → ca. 09:00 Berlin (nicht UTC)
 - [ ] Cron-Plan löschen → keine weiteren Sends
+- [ ] Alten Cron-Eintrag (jobId `repeat:…`) im Dashboard löschen → kein API-Error -8
 - [ ] Dark Mode: Cron-Feld und datetime-local lesbar/bedienbar