Adds a ja locale entry (828 keys) under static/i18n.js LOCALES,
inserted between en and ru. All existing keys translated to natural
concise Japanese suitable for UI labels, with placeholders ({0}, etc.)
and template literals preserved verbatim.
- _lang: 'ja', _label: '日本語', _speech: 'ja-JP'
- 828 keys (matches en, including the documented duplicate keys
whose JS last-wins semantics are preserved)
- syntax verified with `node -c static/i18n.js`
Tested live on a self-hosted instance; Settings → Language → 日本語
selects the new locale and switches the UI text.
14da297cd6
