feat: ignore <style> tag content in markdown

[SoonIter]

Summary

• Backport feat: ignore <style> tag content in markdown #3 to the v18 branch.
• Ignore <style> nodes during Markdown serialization so CSS content is omitted from SSG-MD output.
• Add a regression test for <style> handling on React 18.

Testing

• pnpm install --frozen-lockfile
• pnpm test
• pnpm exec biome check .
• pnpm build

[Copilot]

Pull request overview

Backports behavior to React 18 branch so <style> nodes are skipped during Markdown serialization, preventing CSS from leaking into SSG-MD output.

Changes:

• Update the Markdown serializer to omit <style> elements from output.
• Refactor child-Markdown generation to be lazily evaluated.
• Add a React 18 regression test ensuring <style> content is ignored.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/react/render.ts	Adds style handling to return empty output and refactors child markdown computation to be lazy.
src/react/render.test.tsx	Adds an inline snapshot regression test asserting <style> content is omitted.

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