feat: add per-library download detection auto-schedule

Adds a configurable schedule (manual/hourly/daily/weekly) for the
download detection job in the library settings modal. The indexer
scheduler triggers the job automatically, and the API job poller
processes it — consistent with the reading_status_push pattern.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/backoffice/lib/i18n/en.ts

@@ -202,6 +202,9 @@ const en: Record<TranslationKey, string> = {
   "libraryActions.readingStatusProviderDesc": "Syncs reading states (read / reading / planned) with an external service",
   "libraryActions.readingStatusPushSchedule": "Auto-push schedule",
   "libraryActions.readingStatusPushScheduleDesc": "Automatically push reading progress to the provider on a schedule",
+  "libraryActions.sectionProwlarr": "Download detection",
+  "libraryActions.downloadDetectionSchedule": "Auto-detection schedule",
+  "libraryActions.downloadDetectionScheduleDesc": "Automatically run missing volume detection via Prowlarr on a schedule",
 
   // Reading status modal
   "readingStatus.button": "Reading status",

apps/backoffice/lib/i18n/fr.ts

@@ -200,6 +200,9 @@ const fr = {
   "libraryActions.readingStatusProviderDesc": "Synchronise les états de lecture (lu / en cours / planifié) avec un service externe",
   "libraryActions.readingStatusPushSchedule": "Synchronisation automatique",
   "libraryActions.readingStatusPushScheduleDesc": "Pousse automatiquement la progression de lecture vers le provider selon un calendrier",
+  "libraryActions.sectionProwlarr": "Détection de téléchargements",
+  "libraryActions.downloadDetectionSchedule": "Détection automatique",
+  "libraryActions.downloadDetectionScheduleDesc": "Lance automatiquement la détection de volumes manquants via Prowlarr selon un calendrier",
 
   // Reading status modal
   "readingStatus.button": "État de lecture",