[ui] Replace <img> tags with Next.js <Image> in contributors and profile pages

[AditthyaSS]

Several pages use raw tags for user avatars, causing LCP warnings in the build output.
These should be replaced with Next.js for automatic optimisation.

Affected files:

• src/app/contributors/page.tsx — lines 153, 177, 201, 276
• src/app/u/[username]/page.tsx — line 266
• src/components/layout/Navbar.tsx — user avatar img

How to fix:

// Before
<img src={user.avatarUrl} alt={user.name} className="w-8 h-8 rounded-full" />

// After
import Image from "next/image";
<Image src={user.avatarUrl} alt={user.name} width={32} height={32} className="rounded-full" />


next.config.js already has remotePatterns: [{ protocol: 'https', hostname: '**' }] so all external image URLs are already allowed.

Acceptance criteria:

 All <img> tags for user avatars replaced with <Image>
 No new @next/next/no-img-element warnings in the build output
 Avatars still render correctly at all sizes

[Muskankr]

Hi @AditthyaSS, I would like to work on this issue as NSOC'26 Contributor. Could you please assign this to me?