Multi-box bare-metal Kura with per-account DNS routing and warm-handoff account moves

Operators running Kura on bare metal can now scale a region to multiple boxes instead of being limited to a single box. The controller publishes a per-account A-record that points each account’s hostname at the specific box its pods run on, so traffic for an account always reaches the right box and no longer round-robins across boxes that do not host its pod. Rebalancing an account from a hot box to another is now a warm handoff: a new server is provisioned on the destination box, warms its caches from the source over the account peer plane while the source keeps serving, and is promoted once it has caught up. The customer host has a single owner throughout the move, and the source drains and is destroyed, so there is no cold-cache dip for customers during a rebalance.