feat(cli): provide shell completion scripts

[salim-b]

Closes #262

This PR implements shell completion scripts as requested in #262 for Bash, Zsh, Fish, PowerShell, and Elvish.

[DavisVaughan]

This is looking very nice! I've tweaked it a bit to align more with what ruff does for some ecosystem consistency, added more tests, and tweaked LogLevel so we get completions for its variants.

It's now a hidden top level command of air generate-shell-completion <shell>, which is what ruff does as well to avoid top level namespace pollution in the help output for such a rarely used function.

We should also follow up on our Homebrew formula and tweak it so that it auto generates the completions for the user. I think that is pretty easy to do if we copy ruff:
https://github.com/Homebrew/homebrew-core/blob/b0aa782cf352742b2a1d2add52e6a38aad19b6d9/Formula/r/ruff.rb#L22

Screen.Recording.2026-03-10.at.2.57.11.PM.mov

[salim-b]

Perfect! Thanks for the feedback and going ahead and implementing the desired changes. I'm fine with either subcommand name and all the other changes totally make sense.

We should also follow up on our Homebrew formula and tweak it so that it auto generates the completions for the user.

I decided to give implementing shell completions a shot when I submitted air to conda-forge (still pending) and rediscovered my own issue 😄 I'll surely add shell completions support to the conda-forge recipe once this is released. I'm not too familiar with brew, so I would certainly leave it to you first to file a PR. 🙂