feat(i18n): fix missing translations and implement locale parity checks

[Folex1275]

Fix Spanish/Hebrew stellarErrors and Arabic orphaned keys

Closes #934
Closes #935

Context

Spanish and Hebrew locales were missing 30 stellarErrors translation keys, causing users to see raw technical error codes (like tx_bad_seq, op_underfunded) instead of localized messages when transactions fail. Arabic locale contained 84 orphaned keys from renamed/removed UI elements. No CI check existed to prevent future locale drift.

Outcome

• Spanish and Hebrew now have complete stellarErrors coverage (30 keys added to each)
• Arabic cleaned up (84 orphaned keys removed)
• All 6 locale files now have exact key parity with en.json (468 keys each)
• CI check prevents future locale drift automatically

Details

Added stellarErrors translations:

• frontend/src/i18n/locales/es.json - 30 Spanish translations
• frontend/src/i18n/locales/he.json - 30 Hebrew translations

Removed orphaned keys:

• frontend/src/i18n/locales/ar.json - Removed 84 keys (confirmation, qr, security, advanced, replay, and other deprecated namespaces)

Added CI automation:

• scripts/check-locale-parity.js - Validates key parity (exits 1 on drift)
• scripts/list-locale-diff.js - Debug helper for missing/extra keys
• tests/i18n/locale-parity.test.js - Vitest test suite
• package.json - Added test:locale-parity to CI pipeline
• frontend/src/i18n/locales/README.md - Maintenance guide

Verification:

$ npm run test:locale-parity
✅ All locale files have matching keys!

✓ ar.json: 468 keys (0 missing, 0 extra)
✓ es.json: 468 keys (0 missing, 0 extra)
✓ fr.json: 468 keys (0 missing, 0 extra)
✓ he.json: 468 keys (0 missing, 0 extra)
✓ pt.json: 468 keys (0 missing, 0 extra)
✓ zh.json: 468 keys (0 missing, 0 extra)

Testing

1. Locale parity check: npm run test:locale-parity ✅
2. All locale files validated against en.json ✅
3. Spanish/Hebrew translations verified for tone and consistency ✅
4. Arabic orphaned namespaces confirmed removed ✅
5. CI integration tested ✅

[drips-wave]

@Folex1275 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits