Introduces internal/provider/kvm with the side-effect-free pieces of the provider: providerID format/parse, the namespaced <metadata> element that carries the GC contract, q35 domain XML over pool volumes, volume XML for overlays and raw seeds, the NoCloud seed ISO built with kdomanski/iso9660, and config defaults. All unit-tested. Step 2 of docs/plans/2026-09-04-1404-kvm-provider.md. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>