Scaffold backend gateway and integration docs

lib/core/utils/time_provider.dart

@@ -0,0 +1,9 @@
+import 'package:clock/clock.dart';
+
+/// Shared clock helper for deterministic testing.
+class TimeProvider {
+  TimeProvider._();
+
+  /// Current wall-clock time.
+  static DateTime now() => clock.now();
+}