* feat(sync): prevent deleted "ghost chapters" from reappearing during sync.
- Pass lastSyncTime down to mergeChapters in SyncService.kt.
- Apply timestamp-based tombstoning logic to chapter merging. When a chapter is missing from either the local or remote backup, its `lastModifiedAt` timestamp is checked against the device's last sync time.
- Ensure that chapters deleted on one device (or removed by a source) are recognized as deletions and dropped from the merged backup, rather than being erroneously restored as "new" chapters on subsequent syncs.
* chore: change timestamp to use duration-based calculations
* chore: spotless
KaiserBh
e96895345e