Add syntax highlighting and copy button to code blocks

[Irozuku]

Summary

Enhances the code display experience in the TextMessage component by adding syntax highlighting for markdown code blocks and a copy-to-clipboard feature.

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Type of Change

Check all that apply like this [x]:

• Backend change
• Frontend change
• CI / Workflow change
• Build / Packaging change
• Bug fix
• Documentation

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Changes (by file)

• TextMessage.jsx: Added syntax highlighting for code blocks using react-syntax-highlighter, including dynamic theming for dark/light modes. Implemented a CopyButton component to allow copying code snippets with visual feedback.
• package.json: Added react-syntax-highlighter dependency.

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Testing (optional)

• Verify that code blocks render with proper syntax highlighting in both dark and light modes.
• Ensure the copy button correctly copies code to the clipboard and provides visual feedback.