Notification rate limiting (#110)

* Add notification rate limiting with privacy-safe debug logging

- Add batching system to prevent notification storms (3s rate limit, 5s batch window)
- Queue rapid notifications and show batch summaries
- Debug logs show device names for adverts, sender/channel for messages (no content leaks)
- Remove unused _maxBatchSize constant

Context: Added after getting notification-flooded while evaluating RF flood management. The irony.

* Update notification_service.dart

I made a mistake and removed this

* Add l10n support for notification strings

Addresses PR #110 review feedback to use the translations system:
- Add notification strings to app_en.arb (plurals for batch summary)
- Update NotificationService to use lookupAppLocalizations()
- Wire locale from MaterialApp to NotificationService
- Regenerate localization files

New strings added (English only, translations needed):
- notification_activityTitle: "MeshCore Activity"
- notification_messagesCount: "{count} message(s)"
- notification_channelMessagesCount: "{count} channel message(s)"
- notification_newNodesCount: "{count} new node(s)"
- notification_newTypeDiscovered: "New {type} discovered"
- notification_receivedNewMessage: "Received new message"

* Add notification string translations for all supported languages

Translated notification_activityTitle, notification_messagesCount,
notification_channelMessagesCount, notification_newNodesCount,
notification_newTypeDiscovered, and notification_receivedNewMessage
to: bg, de, es, fr, it, nl, pl, pt, ru, sk, sl, sv, uk, zh

Includes proper ICU plural forms for Slavic languages (few/many/other)
and Slovenian dual form.

* Apply dart format to notification_service.dart

---------

Co-authored-by: Winston Lowe <wel97459@gmail.com>

lib/l10n/app_localizations_zh.dart

@@ -2625,6 +2625,32 @@ class AppLocalizationsZh extends AppLocalizations {
   @override
   String get contacts_contactAdvertCopyFailed => '将广告复制到剪贴板操作失败。';
 
+  @override
+  String get notification_activityTitle => 'MeshCore 活动';
+
+  @override
+  String notification_messagesCount(int count) {
+    return '$count 条消息';
+  }
+
+  @override
+  String notification_channelMessagesCount(int count) {
+    return '$count 条频道消息';
+  }
+
+  @override
+  String notification_newNodesCount(int count) {
+    return '$count 个新节点';
+  }
+
+  @override
+  String notification_newTypeDiscovered(String contactType) {
+    return '发现新 $contactType';
+  }
+
+  @override
+  String get notification_receivedNewMessage => '收到新消息';
+
   @override
   String get settings_gpxExportRepeaters => '导出重复器/房间服务器到GPX';