Moves the three incus_network resources into a dedicated module called once per entry in var.incus_networks. State was migrated imperatively via `terraform state mv` because lxc/incus v1.0.2 does not implement ResourceWithMoveState, making declarative moved blocks unsupported. Plan confirms zero creates/destroys after migration. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>