installer: write custom icon into Minecraft launcher profile

Minecraft launcher's "설치 설정" screen reads `profile.icon` from
launcher_profiles.json. We were leaving it unset, so the launcher fell
back to the default Furnace icon. Inline build/icon.png as a base64
data URL at build time (scripts/build-launcher-icon.cjs generates
src/installer/launcherIcon.ts) and set it on the profile we write.

The build/ directory isn't included in the electron-builder asar (it's
only used to point at the .ico for the exe), so a runtime read isn't
possible — the icon ships compiled into the bundle. To refresh after
changing icon.png, run `npm run build:launcher-icon` (it's wired into
`dist:win` so a fresh exe build always regenerates it).

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "minecraft-music-quiz-installer",
-  "version": "0.2.5",
+  "version": "0.2.6",
   "description": "마인크래프트 음악퀴즈 간편설치기 + 관리 사이트",
   "main": "dist/installer/main.js",
   "scripts": {
@@ -10,7 +10,8 @@
     "installer": "tsc -p tsconfig.installer.json && electron .",
     "installer:rp": "tsc -p tsconfig.installer-rp.json && electron dist/installer-rp/main.js",
     "preinstall:sharp-win32": "npm install --no-save --force @img/sharp-win32-x64@0.34.5",
-    "dist:win": "npm run preinstall:sharp-win32 && tsc -p tsconfig.installer.json && electron-builder --win --config electron-builder.yml",
+    "build:launcher-icon": "node scripts/build-launcher-icon.cjs",
+    "dist:win": "npm run preinstall:sharp-win32 && npm run build:launcher-icon && tsc -p tsconfig.installer.json && electron-builder --win --config electron-builder.yml",
     "dist:win:rp": "npm run preinstall:sharp-win32 && tsc -p tsconfig.installer-rp.json && electron-builder --win --config electron-builder-rp.yml"
   },
   "dependencies": {