feat: Implement self advertisement functionality and enhance location broadcasting settings

lib/providers/connection_provider.dart

@@ -415,6 +415,29 @@ class ConnectionProvider with ChangeNotifier {
     }
   }
 
+  /// Send self advertisement to mesh network
+  ///
+  /// Broadcasts the device's current advertisement data (name, location, etc.)
+  /// to the mesh network. Use this after updating position or name to notify
+  /// other nodes of the change.
+  ///
+  /// [floodMode] - if true, broadcast to entire mesh (default for SAR ops)
+  ///               if false, only send to direct neighbors (zero-hop)
+  Future<void> sendSelfAdvert({bool floodMode = true}) async {
+    if (!_bleService.isConnected) {
+      _error = 'Not connected to device';
+      notifyListeners();
+      return;
+    }
+
+    try {
+      await _bleService.sendSelfAdvert(floodMode: floodMode);
+    } catch (e) {
+      _error = 'Failed to send advertisement: $e';
+      notifyListeners();
+    }
+  }
+
   /// Set radio parameters
   Future<void> setRadioParams({
     required int frequency,

lib/providers/contacts_provider.dart

@@ -9,6 +9,31 @@ import '../services/cayenne_lpp_parser.dart';
 class ContactsProvider with ChangeNotifier {
   final Map<String, Contact> _contacts = {};
 
+  // Add default public channel on initialization
+  ContactsProvider() {
+    _ensurePublicChannelExists();
+  }
+
+  /// Ensure public channel always exists in the list
+  void _ensurePublicChannelExists() {
+    const publicChannelKey = 'public_channel_0';
+    if (!_contacts.containsKey(publicChannelKey)) {
+      // Create a pseudo-contact for the public channel
+      _contacts[publicChannelKey] = Contact(
+        publicKey: Uint8List.fromList(List.filled(32, 0)), // Zero key for public
+        type: ContactType.room,
+        flags: 0,
+        outPathLen: 0,
+        outPath: Uint8List(64),
+        advName: 'Public Channel',
+        lastAdvert: DateTime.now().millisecondsSinceEpoch ~/ 1000,
+        advLat: 0,
+        advLon: 0,
+        lastMod: DateTime.now().millisecondsSinceEpoch ~/ 1000,
+      );
+    }
+  }
+
   List<Contact> get contacts => _contacts.values.toList();
 
   List<Contact> get chatContacts =>
@@ -17,8 +42,11 @@ class ContactsProvider with ChangeNotifier {
   List<Contact> get repeaters =>
       contacts.where((c) => c.isRepeater).toList()..sort(_sortByLastSeen);
 
-  List<Contact> get rooms =>
-      contacts.where((c) => c.isRoom).toList()..sort(_sortByLastSeen);
+  List<Contact> get rooms {
+    // Always ensure public channel exists when getting rooms
+    _ensurePublicChannelExists();
+    return contacts.where((c) => c.isRoom).toList()..sort(_sortByLastSeen);
+  }
 
   /// Get contacts with location (for map display)
   List<Contact> get contactsWithLocation =>