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>

src/server/middleware/auth.ts

@@ -0,0 +1,19 @@
+import type { Request, Response, NextFunction } from 'express'
+
+declare module 'express-session' {
+  interface SessionData {
+    userId?: string
+  }
+}
+
+export function requireAuth(req: Request, res: Response, next: NextFunction): void {
+  if (req.session?.userId) {
+    next()
+    return
+  }
+  if (req.method === 'GET') {
+    res.redirect('/op')
+    return
+  }
+  res.status(401).send('인증이 필요합니다.')
+}