Implements i18n translations for Header component elements using `t` function and adds a missing translation in `ar.json`. Replit-Commit-Author: Agent Replit-Commit-Session-Id: 5a4f78b4-6a2e-4391-b005-5544e086dac8 Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/9777c70b-fc38-4831-8d6b-78dfffe041b0/c8675744-6bc9-4464-806b-f920c1471265.jpg