v0.6.0-rc1: slice 6 Phase A — backup + the self-restore-test (local target)

The guest-level backup layer + the journaled self-restore-test (restore→boot→verify→
teardown) that closes "a backup you haven't restored isn't a backup". All benign
(reuses the slice-4 classifier/gate/journal; no new destructive class/crypto). Local
target only; PBS = Phase B. Restore to a NEW guest only. Backups crash-consistent.

- proxmox: DestroyLXC, VzdumpOptions.Notes (notes-template), LatestBackupVolID.
- reconcile: Engine.RunRestoreTest (journal Scratch entry BEFORE mutation; net link-down
  pre-boot; defer teardown always; benign gated destroy) + Recover extended to reap a
  leaked scratch guest (Scratch flag, special-cased before the UPID path; idempotent).
- internal/backup: runner (vzdump + archive resolve + bulk-gap = backup!=1) + cadence
  scheduler (4th daemon goroutine, default 24h) + in-memory report store.
- hub: Backup/RestoreTest filled; collector seams; cross-repo golden byte-identical +
  bidirectional key-set tests; hub handler logs a FAILED restore-test prominently.
- config BackupConfig (band 990000-990009 default); --selftest=backup / restore-test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/hub/contract_test.go

@@ -46,7 +46,19 @@ func TestHostReport_ContractMatchesGolden(t *testing.T) {
 				Smart: SmartSummary{Health: SmartUnknown},
 			},
 		},
-		Backups: []Backup{}, RestoreTests: []RestoreTest{},
+		Backups: []Backup{
+			{
+				TargetID: "local", VMID: 9001, Archive: "local:backup/x.tar.zst", Mode: "snapshot",
+				CrashConsistent: true, SizeBytes: 1, Success: true, StartedAt: "2026-06-09T11:00:00Z",
+				DurationSeconds: 1, UncoveredVolumes: []string{"/mnt/bulk"},
+			},
+		},
+		RestoreTests: []RestoreTest{
+			{
+				SourceArchive: "local:backup/x.tar.zst", SourceTier: "local", ScratchVMID: 990000,
+				Pass: true, Verified: "boot+running", TestedAt: "2026-06-09T11:05:00Z", DurationSeconds: 1,
+			},
+		},
 		PBSSnapshots: []PBSSnapshot{}, AuditTail: []AuditEntry{},
 		Cloudflared:  Cloudflared{Status: "active"},
 	}
@@ -66,6 +78,10 @@ func TestHostReport_ContractMatchesGolden(t *testing.T) {
 	assertSameKeys(t, "storage_targets[0]", gst, sst)
 	assertSameKeys(t, "storage_targets[0].smart", field(gst, "smart"), field(sst, "smart"))
 	assertSameKeys(t, "storage_targets[0].thin_pool", field(gst, "thin_pool"), field(sst, "thin_pool"))
+
+	// slice-6 additions — backups[0] / restore_tests[0] key sets (the bidirectional guard).
+	assertSameKeys(t, "backups[0]", firstElem(golden["backups"]), firstElem(got["backups"]))
+	assertSameKeys(t, "restore_tests[0]", firstElem(golden["restore_tests"]), firstElem(got["restore_tests"]))
 }
 
 // field extracts a nested object value from a decoded JSON map (nil if absent/not a map).