Adds the kvm block to the providers config (SSH access, images map,
machine-type profiles, hosts list) with validation and table tests.
validate() now rejects mismatched type-specific blocks generically via
setBlocks() instead of pairwise checks.
Step 1 of docs/plans/2026-09-04-1404-kvm-provider.md.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>