Post-domain: add keeltrading.com link to the engine README

[eaitbrahim]

PRD §10: the engine repository is otherwise untouched by this workstream. Once the domain is live, add the site link to CodeGateSoftware/keel's README (+ README.ar), which also reinforces the entity sameAs graph (docs/seo/SEO-STRATEGY.md §3).

• Add keeltrading.com to the engine README (EN + AR editions)
• Confirm the site's Organization JSON-LD sameAs already covers the engine repo (it does; re-verify after any org changes)

[eaitbrahim]

Done — engine PR CodeGateSoftware/keel#468 merged: both README mirrors (EN + العربية) now link keeltrading.com right under the language switcher. The funnel's GitHub end now points back at the site.