What does this PR do?

This pull request enhances the rendering of chat history in the UI by adding support for Markdown formatting and improves code modularity. The most important changes include introducing a new MarkdownRenderer component, updating the ChatHistory component to use it, and adding a new dependency for Markdown rendering.

Markdown rendering enhancements:

• New MarkdownRenderer component: Added a utility component in src/ui/utils/markdown-renderer.tsx to render Markdown content using the ink-markdown library. ([src/ui/utils/markdown-renderer.tsxR1-R6](https://github.com/superagent-ai/grok-cli/pull/14/files#diff-005ce32cfd4f531d35e14136e30ad697a9ccab02e95dc4f2a429d812c4cebe42R1-R6))
• Integration in ChatHistory: Updated the ChatHistory component in src/ui/components/chat-history.tsx to use the MarkdownRenderer for rendering chat messages as Markdown if no tool calls are present. ([src/ui/components/chat-history.tsxL62-R76](https://github.com/superagent-ai/grok-cli/pull/14/files#diff-82d2091fe49b119bba0c22185835018b6456bf9c35099c7f30f5ce2abd9b5e86L62-R76))

Dependency updates:

• Added ink-markdown: Introduced the ink-markdown library as a new dependency in package.json to enable Markdown rendering in the terminal. ([package.jsonR34](https://github.com/superagent-ai/grok-cli/pull/14/files#diff-7ae45ad102eab3b6d7e7896acd08c427a9b25b346470d7bc6507b6481575d519R34))

Fixes #13

Checklist

• I tested my changes
• I reviewed my own code