Support building for MAS

Co-authored-by: Fedor Indutny <79877362+indutny-signal@users.noreply.github.com>

scripts/utils/getBuildCreationTimestamp.mjs

@@ -0,0 +1,17 @@
+// Copyright 2026 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+// @ts-check
+import { execSync } from 'node:child_process';
+import { SECOND } from './durations.mjs';
+
+/**
+ * @returns {number}
+ */
+export function getBuildCreationTimestamp() {
+  const unixTimestamp = parseInt(
+    process.env.SOURCE_DATE_EPOCH ||
+      execSync('git show -s --format=%ct').toString('utf8'),
+    10
+  );
+  return unixTimestamp * SECOND;
+}