Add Mermaid Markdown Diagram Support

[teles]

Enable LLM FX to recognize and render Mermaid code blocks as interactive diagrams within the UI. Users will be able to paste standard Mermaid syntax into the chat, and see flowcharts, sequence diagrams, class diagrams, etc., rendered live in the side panel.

Use case example:

sequenceDiagram
    participant User
    participant LLMFX
    User->>LLMFX: Hello Bill, how are you?
    LLMFX-->>User: I'm good thanks!

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This should produce a sequence diagram showing Alice greeting Bob and Bob replying.

Benefits:

• Improves documentation and brainstorming directly within the app
• Allows quick visualization of processes, architectures and decision flows
• Keeps diagrams versioned alongside chat history

Implementation suggestions:

• Use a JavaFX WebView to load the MermaidJS library
• Detect mermaid code fences and pass the content to Mermaid’s API for SVG/HTML generation
• Cache rendered diagrams in the session history for faster reloading