perf: lazy-load images in markdown preview

[shrutig-blip]

Summary

Adds a custom image renderer to the Markdown preview to improve loading performance.

Changes

• Add a custom img renderer in MarkdownPreview
• Set loading="lazy" for off-screen images
• Set decoding="async" for asynchronous image decoding
• Preserve existing image props (src, title, etc.) by spreading the props
• Default missing alt text to "" for accessibility
• Keep using the native <img> element since Markdown images can reference arbitrary user-supplied URLs, making next/image unsuitable

Testing

• npm run lint
• npm run build

[vercel]

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[shrutig-blip]

Hi @Rinava! I've addressed #43 by adding a custom image renderer that lazy-loads Markdown images while preserving the existing props and providing an empty alt fallback. I also kept the native with a scoped lint suppression since the image URLs are arbitrary user-supplied Markdown URLs. I'd appreciate any feedback. Thanks!

[Rinava]

@shrutig-blip same story as #135 — took it over the line myself rather than leave it stuck behind the Prettier reformat. Rebuilt on today's main so the diff is just the six lines that matter; everything else in your old branch was the requote, which main already has.

Kept it faithful to what you wrote — a plain lazy <img> with decoding="async" and an empty-alt fallback, and I left the @next/next/no-img-element disable in with a one-line why: next/image's remote-domain allowlist genuinely can't cover the arbitrary user URLs markdown throws at it, so the plain tag is the right call here. The only real change from yours was the indentation — the original would've tripped format:check.

Verified locally and in CI — format:check, lint, 87/87 tests, and build all green. (Red Vercel check is the usual fork-deploy notice; "Lint and build" is the gate that matters, and it passed.)

Heads-up: force-pushed onto your branch, so git fetch + hard-reset to origin before you touch it locally. Thanks @shrutig-blip — nice small perf win, and sorry for the wait.