Use next/image for images in pr-stats.tsx #50

Problem

components/pr-stats.tsx renders images with a plain <img>:

• lines 265 and 430: member avatars

Plain <img> skips Next.js's resizing, modern formats and lazy-loading, so these avatars download at full size. ESLint flags it (@next/next/no-img-element).

Check it on /pr-stats.

Done when

• Every <img> listed above is a next/image <Image> with explicit width/height (or fill inside a sized, relative parent).
• Remote hosts are already allowed in next.config.ts (github.com, avatars.githubusercontent.com, images.unsplash.com). If you hit a different host, add it there and say so in the PR.
• The page looks the same as before: same size, crop, rounding and hover effects. Add before/after screenshots to the PR.
• npx eslint components/pr-stats.tsx shows no @next/next/no-img-element.
• npm run build passes.

Size: ~5–15 lines.

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