When an MCP server is stopped, mark it as disabled in the client configs

[dmjb]

If an MCP server is stopped but not deleted, it does not get removed from the client configs - this could lead to problems with clients attempting to use tools from stopped servers.

When a server is stopped, update the config to mark it as disabled. This is available in many MCP clients, but we should validate that it works for all clients we support.

Alternative implementation: Delete the MCP server from the client config on stop, and reinstate when the client is restarted.