Weekly release channels for the Tuist Server and Kura

The Tuist Server and Kura images on GHCR now follow the same three-channel release train that the Tuist CLI has been on for a while. Instead of a single stable image cut on every merge, self-hosted operators can pick the channel that matches how close to the edge they want to run.

• ghcr.io/tuist/tuist:X.Y.0-canary.N is published on every merge to main that touches the server. Canaries are the bleeding edge, marked as GitHub prereleases, and never move :latest. Pin them explicitly if you want to track main.
• ghcr.io/tuist/tuist:X.Y.0-rc.N is published every Monday at 06:00 UTC from a releases/server-X.Y.x branch cut off main. Release candidates soak for a week; fixes ride onto the release branch as cherry-pick pull requests before the next -rc.(N+1) is cut.
• ghcr.io/tuist/tuist:X.Y.0 is the stable release, published the following Monday when the previous week's release candidate is promoted. Only stable releases move :latest, and only stable releases are picked up by mise or any other package manager that excludes prereleases by default.

Kura ships on exactly the same cadence: ghcr.io/tuist/kura:X.Y.0-canary.N, -rc.N, and stable move in lockstep with the server's train, and both trains fire on the same Monday morning as the CLI's promote job.

If you currently pin :latest, nothing changes for you today: :latest will keep tracking the newest stable, just on a weekly rhythm rather than a per-merge one. If you want the bleeding edge or a soaked candidate, the new tags are yours to pin.