Interactively toggle MCP servers and tools from the TUI

[Amolith]

I'd like to list potentially many MCP servers in my Crush config. However, too many servers/tools can be detrimental, so I try to use as few as possible at a time and have to edit my config periodically when I want to change that list. I could also create a project dir just for doing things with a particular server or set of servers, but that feels janky and I think Crush can do better.

What about a new Manage MCPs or Manage MCP servers command in the palette for interactively toggling servers and tools in a modal? On execution, it might list the servers with status indicators and display any error messages with a binding to copy the error to the clipboard. One binding, maybe space, could toggle the highlighted server while another, maybe enter, lists its tools in a new dialog where the user can press space to toggle particular tools. The top-level management modal could also be extended to add/delete the servers (#311).

I don't have any thoughts about whether the changes via the modal should be permanent or only for the session beyond "that's something that would need deciding". If those changes via TUI should persist, I'm also not sure whether they should go in the global config or modify the user's config 🤔

This is somewhat related to discussion #311, but that seemed more about adding MCP servers to Crush while this is about managing ones that have already been added.

[nikaro]

I don't have any thoughts about whether the changes via the modal should be permanent or only for the session beyond "that's something that would need deciding". If those changes via TUI should persist, I'm also not sure whether they should go in the global config or modify the user's config 🤔

I would prefer that interactive changes are not persisted in config. I track my configuration files into git and it would annoy me to have a diff each time i toggle a MCP server. But some sort of persistence could be achieved by storing the state in ~/.local/share/crush/crush.json (would be better to have this under ~/.local/state/crush).