fix(jellyfin): fix remote progress sync, seek reporting, and startup sto

- arm active playback before loadfile with loadedMediaPath: null to suppress premature stop events
- force immediate progress report on seek-like position jumps at the mpv time-pos level
- send positionTicks and failed=false in reportStopped payload
- remove EventName from HTTP timeline payloads (websocket-only field)
- add startup grace window to drop stop events before media finishes loading

changes/fix-jellyfin-remote-progress-sync.md

@@ -0,0 +1,4 @@
+type: fixed
+area: jellyfin
+
+- Fixed Jellyfin remote controller visibility and progress syncing for mpv/SubMiner seek jumps, stopped sessions, and startup path changes.