Integrate SyntaxHighlighter to provide code-aware coloring in diff views.
- Add enable_syntax_highlighting option to DiffViewerOptions
- Extract file extension from diff file paths for language detection
- Apply syntax highlighting to addition/deletion/context lines
- Preserve diff background colors while using syntax colors for text
- Add 7 new tests for syntax highlighting functionality
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Co-Authored-By: Claude <noreply@anthropic.com>
