CVE-2026-34178: LXD: Importing a crafted backup leads to project restriction bypass

LXD instance backup import validates project restrictions against backup/index.yaml embedded in the tar archive, but creates the actual instance from backup/container/backup.yaml extracted to the storage volume. Because these are separate, independently attacker-controlled files within the same tar archive, an attacker with instance-creation rights in a restricted project can craft a backup where index.yaml contains clean configuration (passing all restriction checks) while backup.yaml contains security.privileged=true, raw.lxc host filesystem mounts, and restricted device types. The instance is created from the unchecked backup.yaml, bypassing all project restriction enforcement.