Kura cache regions move to bare metal for faster performance and gapless deploys

The Kura cache infrastructure now runs on bare-metal servers, Scaleway Dedibox for eu-central and OVH for the new ca-east region, instead of shared cloud VMs. Users get faster cache performance: local NVMe storage and a dedicated NIC replace network-attached storage on a best-effort shared NIC. Rolling deploys no longer create a cache gap, because a warm standby is promoted when the primary rolls, so there is no write stall and only a brief window of misses on the very newest artifacts, which regenerate automatically. Public hostnames, cluster IDs, and the CLI are unchanged, so the upgrade is transparent. The new ca-east region is currently gated to staging and canary while the OVH integration is validated.