data-saving: implement gate with bypass

- Implement DataSavingGate util (previous commit was only the shell)
- Update ProfilePictureWidget to always load avatars via UniversalImage
  using fileId, bypassing CloudFileWidget and its data-saving check
- Keep larger media under data-saving control
- Add i18n strings for data-saving mode

Signed-off-by: Texas0295 <kimura@texas0295.top>

lib/utils/data_saving_gate.dart

@@ -0,0 +1,27 @@
+import 'package:flutter/material.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:island/pods/config.dart';
+
+
+typedef WidgetBuilder0 = Widget Function();
+
+class DataSavingGate extends ConsumerWidget {
+  final bool bypass;
+  final WidgetBuilder0 content;
+  final Widget placeholder;
+
+  const DataSavingGate({
+    super.key,
+    required this.bypass,
+    required this.content,
+    required this.placeholder,
+  });
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final dataSaving =
+        ref.watch(appSettingsNotifierProvider.select((s) => s.dataSavingMode));
+    if (bypass || !dataSaving) return content();
+    return placeholder;
+  }
+}