fix(jellyfin): subtitle timing, resume progress, and overlay sync

- Add per-stream subtitle delay persistence and auto timeline-offset correction
- Strip server-selected subtitle stream from mpv load URL; suppress plugin subtitle rearm and auto-start during app-managed preload
- Fix resume position lost when mpv resets on stop; use last known position for final progress/stopped reports
- Keep Play vs Resume distinct to avoid early seek race on normal play
- Fix discovery resume when remote play sends StartPositionTicks=0 despite saved progress
- Deduplicate show/hide overlay commands using recorded visibility state
- Rewrite docs-site Jellyfin page around cast-to-device UX

changes/fix-jellyfin-discovery-resume.md

@@ -0,0 +1,4 @@
+type: fixed
+area: jellyfin
+
+- Fixed Jellyfin discovery resume playback when a remote play command sends `StartPositionTicks: 0` despite saved progress on the item.