proxmox: config block, IDs, marks, state mapping, classify, registration

Phase 2 of the proxmox provider plan. Adds the proxmox: config block with
its validation, registers the type in the config allow-list and the
constructor map, and starts internal/provider/proxmox: the api seam and
its data types, providerIDs (vms/<vmid>/<name>) with the UID-derived VMID,
the description mark, state mapping, and error classification.

Tests read the responses captured from pv1-1 in Phase 0 rather than
repeating Proxmox's wording, and every matcher is run against every
captured error so none fires on the wrong message. The contract methods
are Transient stubs until Phases 5 to 7.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

cmd/main.go

@@ -61,6 +61,7 @@ import (
 	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/provider/kubernetes"
 	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/provider/kvm"
 	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/provider/kvm2"
+	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/provider/proxmox"
 	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/provider/registry"
 	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/providerhealth"
 	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/tracing"
@@ -211,8 +212,9 @@ func main() {
 		"gcp": func(ctx context.Context, pc provider.ProviderConfig) (provider.Provider, error) {
 			return gcp.NewWithWireOptions(ctx, pc, gcp.WireLogOptions{FullPayloads: gcpWireFullPayloads})
 		},
-		"kvm":  kvm.New,
-		"kvm2": kvm2.New,
+		"kvm":     kvm.New,
+		"kvm2":    kvm2.New,
+		"proxmox": proxmox.New,
 	})
 	if err != nil {
 		setupLog.Error(err, "Failed to build providers")