Install Tuist through canary, release candidate, and stable channels

CLI distribution is split into three channels with different stability guarantees. Every CLI-touching commit to main continues to publish a canary prerelease (X.Y.0-canary.N). Stable releases are reached deliberately by freezing a line onto a releases/X.Y.x branch, publishing a release candidate (X.Y.0-rc.N), soaking it, and then promoting it to stable (X.Y.Z). The recommended install points at the latest stable release; canary and RC builds are marked as GitHub prereleases so tuist@latest, mise and Homebrew ignore them by default. Backports keep flowing to a stable line through the existing cli-backport.yml. A Release channels docs page documents pinning strategy and backport policy.