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.