installer: force fabric-installer JVM stdout to UTF-8

Korean Windows defaults the JVM's stdout to cp949 (MS949), so the
fabric-installer's Korean status lines came through as mojibake when
Node decoded them as UTF-8 (e.g. "���가져오는중 (org.ow2.asm:asm:9.9)").

Pass -Dfile.encoding/-Dstdout.encoding/-Dstderr.encoding=UTF-8 before
-jar so the JVM writes UTF-8 and our existing utf-8 decode matches.
stdout/stderr.encoding properties take effect on Java 18+;
file.encoding covers older JDKs.

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "minecraft-music-quiz-installer",
-  "version": "0.2.3",
+  "version": "0.2.4",
   "description": "마인크래프트 음악퀴즈 간편설치기 + 관리 사이트",
   "main": "dist/installer/main.js",
   "scripts": {