v0.8.1

TL;DR

• Fixed the macOS release gate (make e2e-release) flaking with a misleading "VM never got an IP": the real cause was the macOS concurrent-VM cap, which the tooling now surfaces instead of hiding.
• The gate now runs exactly one testbed VM at a time and stops it on exit, so a run never leaves an orphaned VM holding a slot.

Fixed

• macOS testbed release gate (test/testbed/, Tart driver) - no shipped
  binary change; release-tooling only.
  • tart run errors (notably "The number of VMs exceeds the system limit",
    the macOS Virtualization.framework concurrent-VM cap) are now surfaced and
    the gate fails fast with the real reason, instead of swallowing the error
    and blaming a DHCP-lease timeout after 120s.
  • The gate waits for SSH to become reachable before provisioning (sshd comes
    up a few seconds after the VM's IP), fixing an intermittent provision-time
    SSH timeout.
  • The gate enforces a single testbed VM: it stops other running testbed VMs
    up front to guarantee a free slot, and stops its own VM on exit
    (success, failure, or interrupt) so a run never orphans a VM.