Build music-quiz installer and management site per spec

Implements the full spec described in README.md:

Management site (Node + TypeScript + Express + EJS):
- Public main page lists packs registered in manifest.json.
- /op login (account.json, internal-only), /op/dashboard manages packs
  with horizontal-scroll cards, add/select-and-delete flow, and the
  /op/dashboard/:packName editor (Mojang release dropdown, dynamic
  mods/resourcepacks lists, platform/RAM fields, file rename).
- Routes for /manifest.json (public) and /file/* (server pack files).
- Middleware blocks /account.json and /manifest/* directory access.

Installer (Electron):
- Five page renderer driven by IPC (preload contextBridge API):
  pack pick → single/multi → server install (path no-Korean check, JDK
  detect, file download, EULA, RAM gating, local web config editor,
  UPnP/port-forward check) → client install (.mc_custom mods +
  resourcepacks + launcher_profiles.json gameDir/javaArgs) → finish
  toggles (server folder, shortcut, server start, launcher start).

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

electron-builder.yml

@@ -0,0 +1,15 @@
+appId: kr.tkrmagid.musicquiz.installer
+productName: MusicQuizInstaller
+directories:
+  output: release
+files:
+  - dist/installer/**
+  - installer/**
+  - package.json
+win:
+  target: nsis
+  artifactName: ${productName}-${version}-Setup.${ext}
+nsis:
+  oneClick: false
+  allowToChangeInstallationDirectory: true
+  perMachine: false