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/screens/map_tab.dart

@@ -2604,6 +2604,7 @@ class _MapTabState extends State<MapTab> with AutomaticKeepAliveClientMixin {
                           context: context,
                           mapRotation: _getMapRotation(),
                           userPosition: _locationService.currentPosition,
+                          estimatedLocations: contactsProvider.estimatedLocations,
                           onTap: (contact) {
                             _showDetailedCompassWithContact(
                               context,