Track output/report/ so remote repo always has the live match_report

The legacy HTML report under output/report/ (match_report.html plus per-beat
ref/src/compare MP4s) is now part of the repository so the remote always
shows the latest preview state. Added gitignore exception. Total ~26 MB on
disk; comparable to the cutter_clips assets we already track.

Auto-regenerated on every match command via _regenerate_cutter_report, so
this stays in sync without manual intervention.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

@@ -52,3 +52,5 @@ output/*
 !output/cutter_stills/**
 !output/cutter_clips/
 !output/cutter_clips/**
+!output/report/
+!output/report/**