Ether 0.2.51

This release fixes Intel VAAPI hardware transcoding on Linux and in Docker,
preserves warm-probed embedded audio and subtitle tracks on Plex detail pages
when quality variants are active, and improves Plex Media Server migration
preview matching.

Transcoding and Docker

• Full Intel VAAPI shader drivers in Docker (amd64): the Docker image now
  installs intel-media-va-driver-non-free and i965-va-driver-shaders
  instead of Debian's stripped intel-media-va-driver / i965-va-driver
  packages. On Intel Gen8–Gen12 GPUs (including HD Graphics 620 / Kaby Lake),
  this restores the EU kernel shaders needed for VAEntrypointEncSlice
  (QVBR / VBR / CBR rate control) and VAEntrypointVideoProc
  (scale_vaapi / tonemap_vaapi GPU video processing) (#13).
• VAAPI rate-control mode probing and fallback: at startup Ether now probes
  which rate-control modes (QVBR, VBR, CBR, CQP) each VAAPI encoder
  (h264_vaapi, hevc_vaapi) supports on the active device. Bare-metal hosts
  using Low-Power-only (VAEntrypointEncSliceLP) or CQP-only VAAPI drivers
  automatically fall back to VBR, CBR, or bitrate-scaled CQP instead of
  failing encoder init with Driver does not support QVBR RC mode (#13).
• VAAPI HDR tone-mapping probe: startup also probes tonemap_vaapi
  alongside scale_vaapi; if the driver supports GPU scaling but rejects
  hardware HDR tone-mapping, Ether tone-maps in software and still encodes on
  the GPU (#13).

Plex Playback and Metadata

• Pre-play audio and subtitle track selectors with variants enabled:
  /library/metadata/<key> now forwards warm-probed MediaInfo streams into
  the Auto variant entry when no resume row is recorded yet, instead of
  overwriting the warm-probed tracks with the variant resolver's single-stream
  estimate (#145).

Migration and Import

• Plex Media Server preview matching and unwatched filtering: full PMS
  previews no longer resolve or emit Unmatched: warnings for unwatched,
  unrated library items that carry no personal watch state, and items with
  opaque plex:// GUIDs now fall back to exact title + year catalog matching
  when external <Guid> tags are absent (#152).