Support creating a mermaid js embedding

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Clear and concise description of the problem

I want to be able to create an embedding directly, specifically the mermaid.js embedding from mermaid markdown.

Suggested solution

When a mermaid markdown block is surrounded by $$ (as this is what is currently returned), we should create the embeding.

Alternative

No response

Additional context

This would be super useful for the mcp server to be able to have an llm generate the mermaid diagram and have it rendered correctly in anytype without any additional steps

No implementation file, entry point, or test is named in the issue. Start by locating the API path responsible for creating embeddings and inspect how markdown blocks are parsed; done means mermaid markdown surrounded by $$ creates a mermaid.js embedding that renders correctly in Anytype.