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_it.dart

@@ -2774,6 +2774,50 @@ class AppLocalizationsIt extends AppLocalizations {
   String get contacts_contactAdvertCopyFailed =>
       'Copia dell\'annuncio nella Clipboard non riuscita.';
 
+  @override
+  String get notification_activityTitle => 'Attività MeshCore';
+
+  @override
+  String notification_messagesCount(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'messaggi',
+      one: 'messaggio',
+    );
+    return '$count $_temp0';
+  }
+
+  @override
+  String notification_channelMessagesCount(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'messaggi del canale',
+      one: 'messaggio del canale',
+    );
+    return '$count $_temp0';
+  }
+
+  @override
+  String notification_newNodesCount(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'nuovi nodi',
+      one: 'nuovo nodo',
+    );
+    return '$count $_temp0';
+  }
+
+  @override
+  String notification_newTypeDiscovered(String contactType) {
+    return 'Nuovo $contactType scoperto';
+  }
+
+  @override
+  String get notification_receivedNewMessage => 'Nuovo messaggio ricevuto';
+
   @override
   String get settings_gpxExportRepeaters =>
       'Esporta ripetitori / server di stanza in GPX';