installer: address vanilla mods preservation, robust map rename, new app icon

Reviewer follow-ups:

1) Preserve mods/ for vanilla packs. `downloadModsFolder` now checks
   `!pack.modsFolder` BEFORE wiping — vanilla packs (no modsFolder) no
   longer clobber a user's hand-curated mods directory. Wipe still runs
   for modded packs to keep different MC versions from colliding.

2) Always rename the extracted map to `saves/<퀴즈이름>/`, regardless of
   the zip's top-level layout. The zip is now extracted into a temp
   directory under saves/, and:
   - if the temp has a single subdirectory, that subdirectory's content
     becomes the world;
   - otherwise the temp dir itself (e.g. level.dat + region/ at root) is
     the world.
   In either case, it is renamed atomically to `saves/<sanitized name>`
   (or `<name>_2` etc. if a user world collides). Marker tracks the
   final folder name for participant cleanup.

User request: replace both .exe icons.

- Added build/icon.ico (multi-size 16/32/48/64/128/256) and build/icon.png
  generated from the new music-note artwork.
- electron-builder.yml: set win.icon, nsis installer/uninstaller icons,
  buildResources=build, include build/icon.* in files for runtime use.
- New electron-builder-rp.yml + dist:win:rp script so the resourcepack
  installer also packages with the same icon.
- BrowserWindow({ icon }) wired in both installer and installer-rp main
  processes so the running window's titlebar/taskbar icon matches.

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

src/installer-rp/main.ts

@@ -98,9 +98,12 @@ function deriveBaseUrl(manifestUrl: string): string {
 }
 
 function createMainWindow(): void {
+  // 메인 설치기와 동일한 아이콘 사용. dev/prod, Windows/기타 분기까지 같은 규칙.
+  const iconPath = path.join(__dirname, '..', '..', 'build', process.platform === 'win32' ? 'icon.ico' : 'icon.png')
   mainWindow = new BrowserWindow({
     width: 900,
     height: 680,
+    icon: iconPath,
     webPreferences: {
       preload: path.join(__dirname, 'preload.js'),
       contextIsolation: true,