Add translation validation scripts for blog app

Add two validation scripts to ensure translation consistency:

1. check-blog-translations.js - validates cross-locale key sync
   - Compares all locales against English reference
   - Reports missing and extra keys per locale
   - Checks for missing translation files

2. check-blog-translation-usage.js - validates translation key usage
   - Scans source files for t('key') and <Trans i18nKey="key">
   - Reports keys used in code that don't exist in translations
   - Optional --unused flag to show potentially unused keys

Scripts are in global scripts/ folder and called via:
- pnpm --filter @hive/blog lint:translations
- pnpm --filter @hive/blog lint:translations:usage

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>