installer-rp: rename fallback pack name musicquiz → resourcepack

Per user request: when outputPackName is empty, fall back to
`<packKey>_resourcepack` instead of `<packKey>_musicquiz`.

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "minecraft-music-quiz-installer",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "description": "마인크래프트 음악퀴즈 간편설치기 + 관리 사이트",
   "main": "dist/installer/main.js",
   "scripts": {