Add a toggleable stats overlay to the Plex player: active mode
(direct/remux/transcode), transport, resolution, codec, bitrate, HLS level,
dropped frames, buffer-ahead, session offset and position — sampled once a
second off the live videoRef + hlsRef (no data layer). Non-modal corner panel,
aria-live polite, dismissable; toggled with 'd', a gauge control-bar button, or
its X. Number-crunching lives in a pure, unit-tested plexStats module. Doubles
as the S1 transcode-verification surface. i18n HU/EN.