[feature] Use `direnv`

[ianlewis]

Use direnv to set local environment variables.

This is really useful for things like uv which have a lot of settings I want to override. direnv can be installed by aqua locally too.

[ianlewis]

Some projects like mise use this style to switch when in different projects. I'm not sure I really like it though since it can lead to unexpected behavior in different setups.