feat: integrate PR winfunc#261 Mermaid rendering support

- Add interactive Mermaid diagram rendering with pan-zoom support
- Implement MermaidRenderer component with fullscreen dialog viewer
- Add global SVG caching strategy with timestamp expiry
- Integrate MermaidCodeBlock into StreamMessage for code blocks
- Add zoom controls and copy-to-clipboard functionality
- Install dependencies: mermaid, @panzoom/panzoom, @types/mermaid
- Resolve cherry-pick conflicts from PR winfunc#261
- Fix duplicate code blocks from automated conflict resolution
- Clean up unused imports and variables

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Co-Authored-By: Claude <[email protected]>

Author: Sallvainian