[WIP] Fix unknown diagram error in Mermaid rendering

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Unknown diagram error</issue_title>
<issue_description>Hi,

I tried running your MCP server in VSCode using the sample Mermaid snippet from Mermaid Live Editor, but when I click the generated link, I get an “Unknown diagram error”.

Could you advise what I might be doing wrong?

Thanks!

Here’s what I used:

flowchart TD
    A[Christmas] -->|Get money| B(Go shopping)
    B --> C{Let me think}
    C -->|One| D[Laptop]
    C -->|Two| E[iPhone]
    C -->|Three| F[fa:fa-car Car]

Input

{
  "mermaid": "flowchart TD\n    A[Christmas] -->|Get money| B(Go shopping)\n    B --> C{Let me think}\n    C -->|One| D[Laptop]\n    C -->|Two| E[iPhone]\n    C -->|Three| F[fa:fa-car Car]",
  "outputType": "png_url"
}

Output Link:
https://mermaid.ink/img/pako:eNpVy7EKwjAURuHdp_hHHfoCDoJNtUuhDt1Chku5NUGbG5JAEeO7SzvpfL4zPWUZLcWModkBwFkrG13KMyWDqjqVljNm8fwqqPetIFkJwfn7YeP1aqDe3aoY2Tr_-GxFbXfvuaDRHYUswfyEYZGCi3Y3K57_go3MBVc90XGiaqQIRdF8ATbHM0c

Screenshot:

</issue_description>

<agent_instructions>尝试帮我解决一下。</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Unknown diagram error #32

---

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.