feat(git-diff): add Lezer-based syntax highlighting
- Add @lezer/highlight and language parsers (JS/TS, JSON, CSS, HTML, Python, Markdown)
- Create syntax-highlighter utility that parses code with Lezer and returns highlight tokens
- Integrate highlighting into diff view with color-coded tokens
- Keywords (purple), strings (green), numbers (orange), functions (blue), types (yellow), etc.
- Highlighting respects add/remove line backgrounds
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
