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_bg.arb

@@ -1569,6 +1569,13 @@
   "contacts_zeroHopContactAdvertFailed": "Неуспешно изпращане на контакт.",
   "contacts_zeroHopContactAdvertSent": "Изпратен контакт по обява.",
   "contacts_contactAdvertCopyFailed": "Копирането на обявата в клипборда не успя.",
+  "notification_activityTitle": "Активност на MeshCore",
+  "notification_messagesCount": "{count} {count, plural, =1{съобщение} other{съобщения}}",
+  "notification_channelMessagesCount": "{count} {count, plural, =1{съобщение в канал} other{съобщения в канали}}",
+  "notification_newNodesCount": "{count} {count, plural, =1{нов възел} other{нови възли}}",
+  "notification_newTypeDiscovered": "Открит нов {contactType}",
+  "notification_receivedNewMessage": "Получено ново съобщение",
+  "contacts_contactAdvertCopyFailed": "Копирането на обявата в клипборда не успя.",
   "settings_gpxExportContactsSubtitle": "Експортира спътници с местоположение в GPX файл.",
   "settings_gpxExportRepeatersSubtitle": "Изпраща повторители / roomserver с местоположение в GPX файл.",
   "settings_gpxExportAll": "Експортирай всички контакти в GPX",
@@ -1585,4 +1592,5 @@
   "settings_gpxExportShareText": "Картинни данни изнесени от meshcore-open",
   "settings_gpxExportShareSubject": "meshcore-open износ на данни за карта в формат GPX",
   "pathTrace_someHopsNoLocation": "Един или повече от хмелите липсва местоположение!"
+
 }