fix(plex): subtitles survive hls.js and a remounted track

hls.js emptied the cues of every text track on the element when a manifest
loaded or the media attached, our own <track> included, so a VTT that loaded
first showed nothing for the session; its subtitle and caption controllers are
no longer built. A remounted default <track> was switched to showing by the
browser after the hide had run, drawing the cues natively under ours; the hide
now follows every added track and mode change.

frontend/src/lib/hlsPort.ts

@@ -12,7 +12,19 @@ export function createHlsPort(handlers: HlsHandlers): HlsPort | null {
   // up with the live-edge timeline → 0 fragments load → a permanent stall. But the seek-restart model
   // means fragment 0 IS the requested content position (`?t=` positioned the server ffmpeg there),
   // so it always starts VOD-style at 0 and buffers forward up to maxBufferLength.
-  const hls = new Hls({ maxBufferLength: 30, enableWorker: true, startPosition: 0 });
+  //
+  // No subtitle or caption controllers (a controller left unset is never built): the subtitles are
+  // a <track> of ours, out of band, and hls.js empties the cues of EVERY text track on the element
+  // when a manifest loads or the media attaches/detaches — ours included, so a VTT that loaded before
+  // the manifest showed nothing for the rest of the session.
+  const hls = new Hls({
+    maxBufferLength: 30,
+    enableWorker: true,
+    startPosition: 0,
+    subtitleTrackController: undefined,
+    subtitleStreamController: undefined,
+    timelineController: undefined,
+  });
   hls.on(Hls.Events.MANIFEST_PARSED, () => handlers.onManifestParsed());
   hls.on(Hls.Events.AUDIO_TRACKS_UPDATED, () => handlers.onAudioTracksUpdated());
   // The delivered bitrate is measured per fragment: the master playlist's own BANDWIDTH is not a