Feature: Commands to enable/disable MCP servers

Follow up features from: https://github.com/dwash96/cecli/pull/361#issuecomment-3707079488
> - The MCP manager should have enable/disable commands (or probably load/remove for naming consistency with skills) that can remove an MCP server/it's associated tools to and from the returned server list and tools list
> - We should add user facing commands for these two internal methods
