feat: add Japanese, Arabic, Hindi, Portuguese locales + new currencies
- 4 new locale files (ja, ar, hi, pt) with 567 keys each - full coverage
- Japanese (日本語): Hiragana/Kanji script
- Arabic (العربية): RTL-ready text
- Hindi (हिन्दी): Devanagari script
- Portuguese (Português): Brazilian Portuguese
- SUPPORTED_LOCALES updated in i18n.js (10 → 14 locales)
- LOCALE_LABELS updated in oikos-locale-picker.js
- New currencies: AED, BRL, INR, SAR added to budget settings
- Service Worker v31: new locale files pre-cached in APP_SHELL
- Docs: README, SPEC.md, BACKLOG.md, CHANGELOG.md updated
Ulas
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