Track file/ test artifacts in repo

Remove file/* from .gitignore so the 음악퀴즈_test pack is reproducible
across clones. The fabric-installer.jar is the real upstream 1.1.1
(205KB); the rest are minimal stub zips/jar built locally.

  file/platforms/fabric-installer.jar          (fabric-installer 1.1.1)
  file/mods/music-quiz/music-quiz-test-mod.jar (stub fabric mod jar)
  file/resourcepacks/music-quiz.zip            (stub resourcepack)
  file/maps/music-quiz-map.zip                 (stub world)
  file/servers/music-quiz-server.zip           (server stub with eula=false)

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

.gitignore

@@ -3,5 +3,3 @@ dist/
 release/
 logs/
 *.log
-file/*
-!file/.gitkeep