Use next/image in author avatar in page.tsx

[vexital-05]

Fixes #195

Replace the author avatar's <img> with next/image and explicit dimensions to address the image lint warning regarding the additional usage or cost from provider due to the possibility of a slower LCP and an higher bandwidth.

Testing

• npx eslint 'app/blog/author/[slug]/page.tsx' passed
• npm run build passed
• npm test passed

Checklist

• I was assigned the issue before I started
• npm run lint and npm run build pass locally
• The diff only touches what the issue asked for

[vercel]

Someone is attempting to deploy a commit to the Geetansh Goyal's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

No pages to screenshot for this change.