feat: Estimate contact location from RSSI + last-hop repeater

For contacts without GPS, estimate their position by:
1. Finding the first-hop repeater from their routing path
2. Estimating distance from RSSI using log-distance path loss model
3. Placing them at a deterministic offset from the repeater

Uses LoRa outdoor path loss exponent (n=3.0) with reference RSSI
-30dBm at 1m. Distance clamped to 10m-50km range. Bearing derived
from contact public key hash for stable positioning.

lib/providers/app_provider.dart

@@ -18,6 +18,7 @@ import '../services/messaging_route_preferences.dart';
 import '../services/nearest_router_selector.dart';
 import '../services/packet_capture_storage_service.dart';
 import '../services/path_history_service.dart';
+import '../utils/rssi_location_estimator.dart';
 import '../services/profiles_feature_service.dart';
 import '../services/route_hash_preferences.dart';
 import '../services/notification_service.dart';
@@ -1175,6 +1176,18 @@ class AppProvider with ChangeNotifier {
         );
       }
 
+      // Estimate location for contacts without GPS using RSSI + last-hop repeater
+      if (senderContact != null &&
+          senderContact.displayLocation == null &&
+          receptionDetailsSnapshot?.rssiDbm != null &&
+          senderContact.routeHasPath &&
+          senderContact.routeHopCount > 0) {
+        _estimateContactLocationFromRssi(
+          contact: senderContact,
+          rssiDbm: receptionDetailsSnapshot!.rssiDbm!,
+        );
+      }
+
       // Check if message is a drawing broadcast
       if (DrawingMessageParser.isDrawingMessage(enrichedMessage.text)) {
         debugPrint('🎨 [AppProvider] Drawing message received, parsing...');
@@ -2003,6 +2016,46 @@ class AppProvider with ChangeNotifier {
     return bytes.map((byte) => byte.toRadixString(16).padLeft(2, '0')).join();
   }
 
+  /// Estimate a contact's location from the last-hop repeater + RSSI distance.
+  void _estimateContactLocationFromRssi({
+    required Contact contact,
+    required int rssiDbm,
+  }) {
+    // Find the first-hop repeater from the contact's path
+    final pathHopCount = contact.routeHopCount;
+    final pathHashSize = contact.routeHashSize;
+    if (pathHopCount <= 0 || pathHashSize <= 0) return;
+
+    // Get first hop hash from path
+    final pathBytes = contact.routePathBytes;
+    if (pathBytes.length < pathHashSize) return;
+    final firstHopHash = pathBytes
+        .sublist(0, pathHashSize)
+        .map((b) => b.toRadixString(16).padLeft(2, '0'))
+        .join()
+        .toLowerCase();
+
+    // Find a repeater whose public key starts with this hash
+    Contact? lastHopRepeater;
+    for (final c in contactsProvider.contacts) {
+      if (c.publicKeyHex.toLowerCase().startsWith(firstHopHash) &&
+          c.displayLocation != null) {
+        lastHopRepeater = c;
+        break;
+      }
+    }
+    if (lastHopRepeater == null) return;
+
+    final estimated = RssiLocationEstimator.estimateFromRepeater(
+      repeaterLocation: lastHopRepeater.displayLocation!,
+      rssiDbm: rssiDbm,
+      contactPublicKey: contact.publicKey,
+    );
+    if (estimated != null) {
+      contactsProvider.setEstimatedLocation(contact.publicKeyHex, estimated);
+    }
+  }
+
   Future<void> _learnPathFromPublicMessage({
     required Contact contact,
     required List<int> pathBytes,

lib/providers/contacts_provider.dart

@@ -128,6 +128,7 @@ class ContactsProvider with ChangeNotifier {
   final Map<String, Contact> _contacts = {};
   final List<SavedContactGroup> _savedContactGroups = <SavedContactGroup>[];
   final Map<String, PendingAdvert> _pendingAdverts = {};
+  final Map<String, LatLng> _estimatedLocations = {};
   final ContactStorageService _storageService = ContactStorageService();
   bool _isInitialized = false;
   bool _isPersisting = false;
@@ -501,13 +502,33 @@ class ContactsProvider with ChangeNotifier {
       ..sort(_sortByLastSeen);
   }
 
+  /// All estimated locations (for passing to map marker service).
+  Map<String, LatLng> get estimatedLocations =>
+      Map.unmodifiable(_estimatedLocations);
+
+  /// Get estimated location for a contact (RSSI-based, near last-hop repeater).
+  LatLng? estimatedLocationFor(String publicKeyHex) =>
+      _estimatedLocations[publicKeyHex];
+
+  /// Set an estimated location for a contact that has no GPS.
+  void setEstimatedLocation(String publicKeyHex, LatLng location) {
+    _estimatedLocations[publicKeyHex] = location;
+    notifyListeners();
+  }
+
+  /// Effective location: own GPS/advert > estimated from RSSI.
+  LatLng? effectiveLocationFor(Contact contact) {
+    return contact.displayLocation ?? _estimatedLocations[contact.publicKeyHex];
+  }
+
   /// Get contacts with location (for map display)
+  /// Includes contacts with estimated locations from RSSI.
   List<Contact> get contactsWithLocation =>
-      contacts.where((c) => c.displayLocation != null).toList();
+      contacts.where((c) => effectiveLocationFor(c) != null).toList();
 
   /// Get chat contacts with location (team members on map)
   List<Contact> get chatContactsWithLocation =>
-      chatContacts.where((c) => c.displayLocation != null).toList();
+      chatContacts.where((c) => effectiveLocationFor(c) != null).toList();
 
   MessageContactLocation? buildMessageContactLocationSnapshot(
     Contact contact, {