i18n: 음악퀴즈 설치기 UI 문구를 locales/installer/ko-kr.json 으로 분리

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

src/installer/preload.ts

@@ -2,6 +2,9 @@ import { contextBridge, ipcRenderer } from 'electron'
 import type { ClientInstallPayload, FetchedPack, RamCheckResult, ServerInstallPayload, PortForwardResult } from './types.js'
 
 const api = {
+  // i18n
+  loadLocale: (): Promise<Record<string, unknown>> => ipcRenderer.invoke('i18n:dict'),
+
   // 1단계
   loadPacks: (manifestUrl?: string): Promise<FetchedPack[]> =>
     ipcRenderer.invoke('packs:load', manifestUrl),