Improve CRM UI

[bdarcus]

As noted in the README, support for multiple candidate selection isn't great.

I do think the ideal long-term solution is for completion UIs to implement something similar to the helm approach; to improve their CRM UIs.

But in the absence of that, I thought I'd point out this suggestion, which could be a reasonable shorter-term improvement, say for inclusion in the wiki.

minad/vertico#1 (comment)

The basic idea is to have a "short" representation of the candidate string that would be used in the CRM prompt.

Could also be useful for #91.

[bdarcus]

No longer needed with #163.