H-5894: Update X handle to hashai

[vilkinsons]

🌟 What is the purpose of this PR?

Points to our updated X handle: x.com/hashai

[cursor]

PR Summary

Updates the Twitter/X embed example to reference the new handle.

• In blocks/embed/variants.json, changed the Twitter example initialHtml from @hashintel to @hashai (x.com/hashai)

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