feat(plex): honest transcode cold-start + encoder in stats (E6 S1d)

Surface the transcode session's runtime facts in the player. The session
response's transcode/hw flags now thread through: the stats overlay's mode row
reads "transcode · GPU" (VAAPI) or "transcode · CPU" (libx264) — the at-a-glance
confirmation of which S1 path engaged — and the initial-load overlay says
"Preparing stream…" instead of "Loading…" for a transcode session, since its
first segment is genuinely slower than a remux and shouldn't read as a hang.

fmtMode (pure, unit-tested) appends the encoder only for a transcode with a known
encoder. i18n HU/EN for the new preparing label. Browser-UAT'd on the XviD
fixture: mode row reads "transcode · CPU" live (software, no render node here).

frontend/src/components/PlexPlayer.tsx

@@ -98,6 +98,9 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
   const aliveRef = useRef(true);
   const wrapRef = useRef<HTMLDivElement>(null);
   const sessionStartRef = useRef(0); // absolute offset the current HLS/direct session begins at
+  // Which encoder the current transcode session ran: true=VAAPI hardware, false=libx264 software,
+  // null=not a transcode. Feeds the stats overlay's mode row ("transcode · GPU" / "· CPU").
+  const hwRef = useRef<boolean | null>(null);
   const durationRef = useRef(0);
   // ≥2 audio tracks → multi-rendition HLS: all tracks ship in one session and hls.js switches audio
   // client-side (no restart). Ref so the stable loadSession/changeAudio callbacks read it fresh.
@@ -117,6 +120,10 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
   // which only covers the INITIAL session load; this covers stalls AFTER playback has started (e.g. the
   // brief cold-ffmpeg rebuffer on auto-advance, now largely prevented by the server-side segment warm-up).
   const [buffering, setBuffering] = useState(false);
+  // The current session re-encodes the video (playable="transcode"). Its cold-start (the first transcode
+  // segment) is genuinely slower than a remux stall, so the initial-load overlay says "Preparing stream…"
+  // instead of the generic "Loading…" — honest, and it stops a warm-up reading as a hang.
+  const [sessionIsTranscode, setSessionIsTranscode] = useState(false);
   const [loadError, setLoadError] = useState<string | null>(null);
   // The current session's real media-start K (reactive mirror of sessionStartRef). Subtitles are
   // absolute-time VTT shifted by K to the session's zero-based clock, so the <track> src/key keys off
@@ -219,6 +226,11 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
         );
         return;
       }
+      // Surface the active mode for the stats overlay + the honest cold-start label: a transcode session
+      // re-encodes the video (hw = which encoder), and its first segment is genuinely slower than remux.
+      const isTranscode = sess.mode === "hls" && !!sess.transcode;
+      hwRef.current = isTranscode ? (sess.hw ?? false) : null;
+      setSessionIsTranscode(isTranscode);
       // hls.js plays our non-zero-start copyts stream ~1s BEHIND the media clock (see HLS_SUB_LAG);
       // fold that into the session start so the seekbar clock, seeking AND the subtitle shift are all
       // content-accurate. Direct-play (start_s 0) uses the file's real clock — no compensation.
@@ -807,7 +819,9 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
                   rebuffer/seek (ready, no error) has no visible label, so give it an sr-only one via the
                   aria-live region so a screen reader distinguishes "buffering" from a frozen frame. */}
               {!ready ? (
-                <span>{t("plex.player.loading")}</span>
+                <span>
+                  {t(sessionIsTranscode ? "plex.player.preparing" : "plex.player.loading")}
+                </span>
               ) : buffering ? (
                 <span className="sr-only">{t("plex.player.buffering")}</span>
               ) : null}
@@ -1183,6 +1197,7 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
           videoRef={videoRef}
           hlsRef={hlsRef}
           playable={detail?.playable ?? ""}
+          hwRef={hwRef}
           sessionStartRef={sessionStartRef}
           absRef={absRef}
           durationRef={durationRef}

frontend/src/components/PlexStatsOverlay.tsx

@@ -12,6 +12,7 @@ export function PlexStatsOverlay({
   videoRef,
   hlsRef,
   playable,
+  hwRef,
   sessionStartRef,
   absRef,
   durationRef,
@@ -20,6 +21,7 @@ export function PlexStatsOverlay({
   videoRef: RefObject<HTMLVideoElement | null>;
   hlsRef: RefObject<Hls | null>;
   playable: string;
+  hwRef: RefObject<boolean | null>; // active transcode encoder: true=GPU, false=CPU, null=not transcode
   sessionStartRef: RefObject<number>;
   absRef: RefObject<number>;
   durationRef: RefObject<number>;
@@ -75,6 +77,7 @@ export function PlexStatsOverlay({
       setRows(
         buildStatRows({
           playable,
+          hwEncoder: hwRef.current,
           transport: hls ? "hls" : "direct",
           videoWidth: v?.videoWidth ?? 0,
           videoHeight: v?.videoHeight ?? 0,
@@ -91,7 +94,7 @@ export function PlexStatsOverlay({
     sample();
     const iv = setInterval(sample, 1000);
     return () => clearInterval(iv);
-  }, [videoRef, hlsRef, playable, sessionStartRef, absRef, durationRef]);
+  }, [videoRef, hlsRef, playable, hwRef, sessionStartRef, absRef, durationRef]);
 
   return (
     <div