Implement logout endpoint on API

[sadeeq6400]

Summary

This PR has fullfilled all the requirements needed

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Related issues

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Closes: #198

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• [ x ] feat
• fix
• docs
• chore
• test
• ci

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cd api
npm run lint
npm run build
npm test

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• I rebased onto origin/main and resolved conflicts.
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[Xhristin3]

Token denylist tied to remaining TTL + guard check on every request is the right shape. Replacing the placeholder X-User-Id header with real JWT validation is a great cleanup too. Tests look good. Merging 🎉