feat(admin): deleted-account dossier + operator delete-user action

The user-detail console gains a Deletion & retention panel: last login (time + IP),
the tombstone (deleted-at + retained real name), and the retention journal (the legal
dossier of detached credentials). A Delete-user action runs the same deletion
orchestration as the in-app flow (mirrors the email-erase pattern). Store readers
RetainedIdentities + DeletionInfo back the view; integration test covers them.

backend/internal/inttest/delete_test.go

@@ -95,6 +95,45 @@ func TestAnonymizeAndTombstone(t *testing.T) {
 	}
 }
 
+// TestDeletionDossierReaders: after deletion the admin readers expose the credential
+// journal and the tombstone dossier.
+func TestDeletionDossierReaders(t *testing.T) {
+	ctx := context.Background()
+	store := account.NewStore(testDB)
+	deleter := accountdelete.NewDeleter(testDB)
+
+	acc, _, err := store.ProvisionTelegram(ctx, "tg-"+uuid.NewString(), "ru", "handle", "Иван", "+03:00")
+	if err != nil {
+		t.Fatalf("provision: %v", err)
+	}
+	if err := store.AttachIdentity(ctx, acc.ID, account.KindEmail, "dos-"+uuid.NewString()+"@example.com", true); err != nil {
+		t.Fatalf("attach email: %v", err)
+	}
+	if err := deleter.AnonymizeAndTombstone(ctx, acc.ID); err != nil {
+		t.Fatalf("delete: %v", err)
+	}
+
+	rets, err := store.RetainedIdentities(ctx, acc.ID)
+	if err != nil || len(rets) != 2 {
+		t.Fatalf("RetainedIdentities = (%+v, %v), want 2 rows", rets, err)
+	}
+	for _, r := range rets {
+		if r.Reason != "delete" {
+			t.Errorf("retained reason = %q, want delete", r.Reason)
+		}
+	}
+	info, err := store.DeletionInfo(ctx, acc.ID)
+	if err != nil {
+		t.Fatalf("DeletionInfo: %v", err)
+	}
+	if info.DeletedAt == nil {
+		t.Error("DeletionInfo.DeletedAt should be set")
+	}
+	if info.DeletedDisplayName != "Иван" {
+		t.Errorf("DeletionInfo.DeletedDisplayName = %q, want Иван", info.DeletedDisplayName)
+	}
+}
+
 // TestDropAllRobotGames drops the deletee's solo vs-AI game but keeps a game with a human
 // opponent.
 func TestDropAllRobotGames(t *testing.T) {