Restore a reinstallable direct agent binary on reset

[Copilot]

Reset retained the managed blue/green symlink layout, forcing the installer to special-case post-reset hosts. This change moves binary restoration into reset while preserving a callable agent command.

• Reset lifecycle

  • Stop the agent and recovery services.
  • Verify inactivity under the shared activation lock.
  • Atomically replace /usr/local/bin/aks-flex-node with the active executable before removing managed slots and links.

• Safe cleanup

  • Reject unexpected symlinks and invalid executables.
  • Remove only known layout entries, preserving unexpected contents.
  • Support direct installations, repeated reset, and interrupted-cleanup retries.

• Installer boundary

  • Remove installer-side managed-layout cleanup.
  • Reinstall through the normal direct-binary path after reset; retain AgentUpgrade for managed installations.

• Fixes Make reset restore a reinstallable direct agent binary #311