chore: restore product scaffold to rollback baseline

apps/chanora_flutter/lib/services/prefetch_debouncer.dart

@@ -0,0 +1,31 @@
+import 'dart:async';
+
+class PrefetchDebouncer {
+  PrefetchDebouncer({
+    required this.onPrefetch,
+    this.delay = const Duration(milliseconds: 700),
+  });
+
+  final Future<void> Function(String host) onPrefetch;
+  final Duration delay;
+
+  Timer? _timer;
+  bool _disposed = false;
+
+  void schedule(String rawHost) {
+    if (_disposed) return;
+    _timer?.cancel();
+    final host = rawHost.trim();
+    if (host.isEmpty) return;
+    _timer = Timer(delay, () {
+      if (_disposed) return;
+      unawaited(onPrefetch(host));
+    });
+  }
+
+  void dispose() {
+    _disposed = true;
+    _timer?.cancel();
+    _timer = null;
+  }
+}