Add KVM provider config: KVMConfig structs and validation

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>

.claude/settings.json

@@ -93,7 +93,13 @@
       "Bash(git -C /Users/jan.novak/srv/go/egress-proxies-operator tag 0.01)",
       "Bash(git -C /Users/jan.novak/srv/go/egress-proxies-operator push origin 0.01)",
       "Bash(chmod +x docs/demo/run-demo.sh)",
-      "Bash(bash -n docs/demo/run-demo.sh)"
+      "Bash(bash -n docs/demo/run-demo.sh)",
+      "Bash(git add *)",
+      "Bash(git commit -q -m 'Add plan: KVM/libvirt provider *)",
+      "Bash(go get *)",
+      "Bash(go build *)",
+      "Bash(go test *)",
+      "Bash(git commit *)"
     ],
     "additionalDirectories": [
       "/Users/jan.novak/srv/go/egress-proxies-operator/.claude",