Fix transcode-hevc hanging on files with attached pictures

Map only the first video stream, all audio, and all subtitles instead
of mapping everything. This avoids feeding cover art images through
the libx265 encoder which caused hangs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/transcode-hevc.sh

@@ -229,7 +229,7 @@ while IFS= read -r -d '' file; do
 
     if "$FFMPEG" -nostdin -y \
         -i "$file" \
-        -map 0 \
+        -map 0:v:0 -map 0:a -map 0:s? \
         -c:v libx265 -crf "$CRF" -preset "$PRESET" \
         -c:a copy \
         -c:s copy \