#501 i18n: add the missing cert.music_links_checkbox key to English and Arabic

[Anonymous]

Originally created by: Redo-San

cert.music_links_checkbox is consumed at Style/pages/certificate/index.html:783 and already exists in de, es, fr, ja, ko, zh — only en and ar are missing it.

Files

• Style/lang/en.json, Style/lang/ar.json
• the 2 regenerated Style/lang/i18n-data-*.js

Acceptance criteria

• [ ] Key present in all 8 .json and all 8 .js files.
• [ ] node scripts/sync-i18n-json-to-js.js runs clean.