Remove MCP/Extension prefix from tool picker categories

[digitarald]

I suggest to remove the "MCP Server: " and "Extension: " prefix from the tool "folders".

It would lighten the dense UI by a lot. What protocol the tools come from doesn't really matter to most users user. We have the icons to clarify the source and the settings icon still opens the right place if they care about where the tools are defined.

[TylerLeonhardt]

I'm cool with this, but @aeschli actually owns this UI (I just provide the Quick Tree).