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_sk.arb

@@ -1569,6 +1569,13 @@
   "contacts_zeroHopContactAdvertFailed": "Zlyhalo odoslanie kontaktu.",
   "contacts_ShareContactZeroHop": "Zdieľať kontakt cez inzerát",
   "contacts_ShareContact": "Kopírovať kontakt do schránky",
+  "notification_activityTitle": "Aktivita MeshCore",
+  "notification_messagesCount": "{count} {count, plural, =1{správa} few{správy} other{správ}}",
+  "notification_channelMessagesCount": "{count} {count, plural, =1{správa kanálu} few{správy kanálu} other{správ kanálu}}",
+  "notification_newNodesCount": "{count} {count, plural, =1{nový uzol} few{nové uzly} other{nových uzlov}}",
+  "notification_newTypeDiscovered": "Nový {contactType} objavený",
+  "notification_receivedNewMessage": "Prijatá nová správa",
+  "contacts_ShareContact": "Kopírovať kontakt do schránky",
   "settings_gpxExportRepeatersSubtitle": "Exportuje repeater / roomserver s lokalitou do súboru GPX.",
   "settings_gpxExportContacts": "Export sprievodcov do GPX",
   "settings_gpxExportSuccess": "Úspešne exportovaný súbor GPX.",
@@ -1585,4 +1592,5 @@
   "settings_gpxExportShareText": "Mapové údaje exportované z meshcore-open",
   "settings_gpxExportShareSubject": "meshcore-open export dát GPX mapových údajov",
   "pathTrace_someHopsNoLocation": "Jedna alebo viac chmeľov chýba lokalita!"
+
 }