Import now always claims the server and rebinds Sentinel. Remove the
SSH-written ownership file, the write_remote/rebind_sentinel/claim
options, and the POST /servers/{uuid}/claim endpoint. The migrator now
fails when the target cannot take management. Disabling management
records transfer.management_disabled so the server shows as
transferable, and the transfer and import pages are simplified.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>