CLI: No ddn model list or something because I don't even know what models to add or update!

Suggestions:

1. `ddn model ls`
2. `ddn model add -i` - interactive mode where I can choose what models to add via some kind of interactive thing
3. `ddn model update -i` - interactive mode where I can choose what models to add via some kind of interactive thing

This is a pretty big blocker because I don't even know what models I have to be able to add them.

For updating models it would be good to see a little `*` to know which models need an update (like a git log thing that shows me)

The issue names no files or tests. Start by reviewing the existing ddn model add and update commands, then determine where model discovery and interactive selection belong. Done means users can list available models, choose models to add or update interactively, and identify models needing updates.

Written by the indexing model from the issue text.