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/api/workloads_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/alexei/tinyforge/internal/auth"
 	"github.com/alexei/tinyforge/internal/crypto"
 	"github.com/alexei/tinyforge/internal/store"
+	"github.com/alexei/tinyforge/internal/volsnap"
 	"github.com/alexei/tinyforge/internal/webhook"
 	"github.com/alexei/tinyforge/internal/workload/plugin"
 
@@ -75,6 +76,7 @@ type apiTestEnv struct {
 	dispatcher *fakeAPIDispatcher
 	adminToken string
 	encKey     [32]byte
+	snapEngine *volsnap.Engine // set by newSnapshotEnv; nil otherwise
 }
 
 func (e *apiTestEnv) close() { e.srv.Close() }
@@ -670,9 +672,9 @@ func TestGetWorkloadChain_ParentSelfChildren(t *testing.T) {
 
 	resp := e.do(t, http.MethodGet, "/api/workloads/"+parentID+"/chain", nil)
 	var got struct {
-		Parent   *map[string]any   `json:"parent"`
-		Self     map[string]any    `json:"self"`
-		Children []map[string]any  `json:"children"`
+		Parent   *map[string]any  `json:"parent"`
+		Self     map[string]any   `json:"self"`
+		Children []map[string]any `json:"children"`
 	}
 	if errMsg := decodeEnvelope(t, resp, &got); errMsg != "" {
 		t.Fatalf("envelope error: %q", errMsg)