Use mcp icon for MCP servers sidebar item

What does this MR do and why?

The Automate > MCP servers item in the project and group super sidebars now uses the new Pajamas mcp icon instead of the generic api icon.

References

Tailored navigation: Concrete fixes and polish ... (#621643)

Screenshots or screen recordings

To be added.

Before	After

How to set up and validate locally

1. Make sure @gitlab/svgs is 3.171.0 or later and run yarn install.
2. In the Rails console, run Feature.enable(:ai_catalog_mcp_servers).
3. Use a top-level group that has GitLab Duo features, MCP enabled for Duo workflows, and experiment and beta features turned on.
4. In a project in that group, in the left sidebar, select Automate. The MCP servers item shows the mcp icon.
5. Open the group itself, select Automate, and check that MCP servers shows the same icon.

MR acceptance checklist

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