Add MCP tools for docs

[piki]

This adds two new tools to pscale mcp server:

• list_docs lists all available docs on planetscale.com/docs
• get_doc retrieves one doc from the output of list_docs, in Markdown format

The funny thing is, I can't get Claude to bother with this tool at all. Here's a sample conversation:

Give me an example of how to add a vector index with cosine distance to a PlanetScale database

It hallucinates something based on vector syntax from several other MySQL-style databases.

That's wrong. Check the docs.

It searches the web and provides a correct answer.

How much memory does my instance need to build a vector index with a million rows? Check the planetscale docs.

It searches the web and provides a correct answer.

In the PlanetScale docs, how do I create a Metal database?

It searches the web and provides a correct answer.

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So, I'm not convinced list_docs and get_docs are necessary -- an LLM that knows how to use those probably knows how to search the web, which accomplishes the same purpose without the ongoing costs of maintaining docs-related MCP tools and endpoints.

I really just opened this for discussion. cc @ayrton