CLI releases now use canary, release candidate, and stable channels

Tuist now supports canary, release candidate, and stable release channels. Canary builds ship on every CLI-touching commit to main, RCs soak on a release branch before promotion, and stable releases become the default recommended install. This decouples fixes from features so tuist@latest moves more slowly and upgrades no longer absorb a batch of unrelated changes. The new channels are documented on the CLI Release channels page.