feat: Add setting to disable map tab for battery savings

Add a new "Disable Map" toggle in settings that allows users to hide
the map tab entirely. This is useful for scenarios where the map is
not needed and battery conservation is a priority.

Changes:
- Add disableMap and disableMapDescription localized strings (all languages)
- Add isMapEnabled state to AppProvider with persistence
- Update HomeScreen to dynamically adjust tab count based on setting
- Make onNavigateToMap optional in MessagesTab and ContactsTab
- Add toggle switch in Settings screen under Interface section

lib/l10n/app_localizations_de.dart

@@ -137,6 +137,13 @@ class AppLocalizationsDe extends AppLocalizations {
   String get simpleModeDescription =>
       'Nicht wesentliche Informationen in Nachrichten und Kontakten ausblenden';
 
+  @override
+  String get disableMap => 'Karte deaktivieren';
+
+  @override
+  String get disableMapDescription =>
+      'Karten-Tab ausblenden, um Akku zu sparen';
+
   @override
   String get language => 'Sprache';