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/shared/nat-upnp.d.ts

@@ -0,0 +1,18 @@
+declare module 'nat-upnp' {
+  interface PortMappingOptions {
+    public: number | { host?: string; port: number }
+    private: number | { host?: string; port: number }
+    ttl?: number
+    description?: string
+    protocol?: 'tcp' | 'udp'
+  }
+
+  interface UpnpClient {
+    portMapping(options: PortMappingOptions, callback: (err: Error | null) => void): void
+    portUnmapping(options: { public: number; protocol?: 'tcp' | 'udp' }, callback: (err: Error | null) => void): void
+    externalIp(callback: (err: Error | null, ip: string) => void): void
+    close(): void
+  }
+
+  export function createClient(): UpnpClient
+}