Refactor ChatView and MessageView for improved performance and UI
- Replace MarkdownUI with custom LazyMarkdownView using MarkdownKit
- Implement custom HTML rendering for better code block display
- Optimize scrolling behavior in ChatView
- Improve message layout and styling
- Add image grid view for multiple images in user messages
- Enhance copy functionality for messages and code blocks
- Update BedrockClient to support new Stable Diffusion models
- Remove unused files (CodeBlockView, SplashCodeSyntaxHighlighter)