Drag in subtitle files alongside .mkv files and they're matched to
the right video by episode code (S04E06, zero-padding and separator
insensitive, plus 4x06 as a fallback) and muxed in as extra subtitle
tracks. Any subtitle format mkvmerge accepts is recognized: SRT,
(S)SA, VobSub, WebVTT, PGS/SUP, USF, SAMI, TTML/DFXP, STL, Kate.
Matching works regardless of drop order — subtitles dropped before
their video are held pending until a matching video shows up, and
vice versa. Language, forced, and SDH flags are guessed from common
filename tokens (e.g. "eng", "forced", "sdh") to set the muxed
track's language/name/flags; unmatched subtitles are reported in the
status bar.
