terms: per-term installer visibility toggles + universal delete (v0.3.4)

- _meta.json: customLabels -> terms.{label,showInInstaller,showInInstallerRp}
- Drop builtin protection; any term kind can be deleted/added/toggled
- New public route /manifest/terms/<pack>/index.json for installer term lists
- Installers fetch terms:list dynamically; skip agreement step if list empty
- Term editor: 2 visibility checkboxes (설치기 / 리소스팩 설치기), multi-select
- Migration from old schema preserves custom labels (default: visible in both)

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "minecraft-music-quiz-installer",
-  "version": "0.3.3",
+  "version": "0.3.4",
   "description": "마인크래프트 음악퀴즈 간편설치기 + 관리 사이트",
   "main": "dist/installer/main.js",
   "scripts": {