Cyrus Setup Repository

This handles the initial setup for Cyrus by registering Git repositories to your config so it can start processing issues from those codebases. It walks you through checking what's already configured, then adds new repos by running `cyrus self-add-repo` which clones them to `~/.cyrus/repos/` and registers them with your Linear workspace. Worth noting the strong security guidance here: it enforces bash-only interactions with config files to keep secrets out of conversation context, which is the right approach for anything touching credentials. You'll use this once per repo when getting Cyrus connected to your projects, and it supports multi-workspace setups if you need that.