Per-project recent models

[plutonium-239]

Description

Currently, the "recently used models" list is global. This is inconvenient.

Say I use crush in a work project with an openrouter model, then afterwards I use crush in a personal project (where I want to use my personal hyper account rather than the work openrouter api key).
So everytime I have to go to the model list and change the model back and forth.

And it makes more sense to tie the model preference to a project rather than globally.

Possible Solutions

Currently, the recent models are stored in the global ephemeral state at ~/.local/share/crush/crush.json. This can easily be made per project by either:

1. Shifting the recent models list to ~/.local/share/crush/projects.json, which already contains every single project where crush is used.
2. Making a new entry in ~/.local/share/crush/crush.json which is an object mapping every project to its recent models list.
3. Making a new file in $project/.crush/