feat(i18n): add bilingual support (EN/ES) and missing keys CI check

[queentiffany1111-cloud]

succesfully implemented

closes #77

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[truthixify]

Hey @queentiffany1111-cloud, thanks for the bilingual work. Your build is failing at lint:i18n with 180 key mismatches between the two locale files:

• 4 keys in en.json are missing from es.json (e.g. careers.signup.errorDefault, notFound.error404, pressPage.labels.failed, stellarPage.codeSection.failed)
• 171 keys in es.json are missing from en.json — this suggests you added a lot of new content only in Spanish, and en.json needs matching entries

The lint script requires both files to have identical key sets. Add the missing entries on both sides and CI should go green. Vercel is also failing but that's non-blocking, will merge on green build.