Make connection failure to ctp more understandable

[cwilhit]

What problem are you facing?

Prematurely trying to connect to an MCP that's in a creating state could be handled more gracefully from up

How could Upbound help solve your problem?

Example of what's returned when trying to (intentionally) connect to an MCP that's not ready yet:

It would be great to do a few things:

1. At a minimum, reflect a more user-friendly error that it can't connect to the MCP because it's still creating and isn't ready yet.
2. If using the TUI, maybe we could disallow trying to set context to an MCP in a creating state (reflect this in the TUI? Get fancy with a creating animation next to the MCP entry name? Or a label like [creating]