feat: support codeblock syntax highlighting

[Yukaii]

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Summary by cubic

Adds syntax highlighting for code blocks via a simple codeHighlighter API. This enables real-time, library-agnostic highlighting with examples for Shiki and highlight.js.

• New Features
  • New codeHighlighter API: set globally (OverType.setCodeHighlighter(fn)) or per instance (codeHighlighter option).
  • Real-time highlighting for fenced code blocks while preserving character alignment.
  • Examples: shiki-integration.html and highlightjs-integration.html.
  • Docs: SYNTAX_HIGHLIGHTING.md with setup and usage.

[MathiasWP]

+1 on this!

[vuthanhtrung2010]

+1

[jippi]

Any plans to land this? ❤️

[panphora]

Syntax highlighting is now available in v2.0.1! 🎨

We've implemented a library-agnostic approach that works with Shiki, Highlight.js, Prism, or any custom highlighter:

// Global highlighter
OverType.setCodeHighlighter((code, language) => {
  return highlighter.highlight(code, { language }).value;
});

// Or per-instance
new OverType('#editor', {
  codeHighlighter: myHighlighter
});

Key features:

• Synchronous highlighters only (Shiki works if you await setup first, then use the highlighter object synchronously)
• Character-by-character alignment verified with comprehensive tests
• All three major libraries (Shiki, Highlight.js, Prism) tested and confirmed working
• See docs/SYNTAX_HIGHLIGHTING.md and examples in website/examples/

Thanks for the initial implementation! We built on your foundation and added alignment verification to ensure OverType's core cursor alignment remains perfect.