feat(packages): add ai-assistant package with Codex CLI, Claude (Anthropic) and Gemini (Google) integrations; UI panel, settings, menu, keybinding

[heyfinal]

[savetheclocktower]

Thanks for the contribution!

I would encourage you to publish this package to the package repository. In the rare cases where Pulsar (and Atom before it) accepted brand-new packages into the core, they almost always started out as community packages.

Personally, I am happy for Pulsar to have packages available for various LLM integrations; but to me it's unlikely that any such package would ever be bundled into the core.