If the base resourcepack already has audio files under
assets/musicquiz/sounds/ or entries in assets/musicquiz/sounds.json,
the build now PRESERVES them and skips any new track that would
collide. Same policy for painting textures: existing cover_*.png
in the base are not overwritten by new ones.
Per-track collision is logged so the user can see exactly what was
preserved and what was skipped. Summary counts (added / skipped)
are also logged.
Requested by 사금향: "기존에 있는걸 삭제하거나 이상하게 엎어쓰지
말것" — preserve base assets unconditionally.