rp-pack: never overwrite base resourcepack sounds/paintings (v0.3.5)

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.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "minecraft-music-quiz-installer",
-  "version": "0.3.4",
+  "version": "0.3.5",
   "description": "마인크래프트 음악퀴즈 간편설치기 + 관리 사이트",
   "main": "dist/installer/main.js",
   "scripts": {