feat(volsnap): volume snapshot restore (backlog #6)

Restore a captured volume snapshot onto an image workload's live host-bind
data volumes, then redeploy — the most destructive workload action, built to
the adversarially-reviewed design (C1–C6) with all data-loss guards.

- Engine.Restore (engine-owned): all-or-nothing pre-flight re-resolution from
  the workload's CURRENT config (never the tamperable manifest), per-filesystem
  disk pre-check, per-workload lock, container quiesce, extract-to-tmp, durable
  pre-restore snapshot, write-ahead journal, atomic rename swap, redeploy, and
  crash-recovery sweep (RecoverInterruptedRestores) wired before serving.
- internal/keyedmutex: shared per-key lock; deployer now serializes every
  deploy entrypoint per workload via DispatchPlugin (+ LockWorkload/RedeployLocked
  for the restore re-dispatch, no deadlock).
- Untrusted-archive extractor: zip-slip containment, type allow-list (reg/dir
  only), decompression-bomb cap, manifest-index bounds.
- POST /api/workloads/{id}/snapshots/{sid}/restore: admin, X-Confirm-Restore
  header (CSRF), per-workload single-flight (409).
- WebUI: Restore button + danger ConfirmDialog + busy state + i18n (en/ru).

Scope: image-source only; scopes absolute/stage/project (driven off the same
supportedScopes constant capture uses).

Plan-reviewed before coding; per-phase go/security/ts reviews; final review
READY TO MERGE. Security review caught + fixed a CRITICAL manifest-Source path
traversal (re-derive target from current config + base containment).

Plan: plans/volume-snapshot-restore/

internal/volsnap/disk_windows.go

@@ -0,0 +1,24 @@
+//go:build windows
+
+package volsnap
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/windows"
+)
+
+// freeDiskBytes returns the bytes available to the caller on the volume backing
+// path (used by the restore disk pre-check, C5). Windows is the dev platform;
+// production runs on Linux (see disk_unix.go).
+func freeDiskBytes(path string) (uint64, error) {
+	p, err := windows.UTF16PtrFromString(path)
+	if err != nil {
+		return 0, fmt.Errorf("encode path %s: %w", path, err)
+	}
+	var freeAvail, total, totalFree uint64
+	if err := windows.GetDiskFreeSpaceEx(p, &freeAvail, &total, &totalFree); err != nil {
+		return 0, fmt.Errorf("GetDiskFreeSpaceEx %s: %w", path, err)
+	}
+	return freeAvail, nil
+}