Managed Kura regions use per-environment hostnames to avoid cross-environment collisions

Managed Kura regions now get environment-scoped public hostnames, so staging and canary nodes no longer share the same DNS record as production and collide into the production cluster. Non-production regions get a -staging or -canary suffix in the leftmost label of their *.kura.tuist.dev hostname, while production stays unchanged. Existing nodes are re-applied automatically, and stale cache endpoint rows that still pointed to the old production host are pruned on staging and canary only.