Add automatic nearby discovery and simplify device presence UI

.env.example

@@ -11,6 +11,8 @@ DATABASE_PATH=/data/database/hop.sqlite
 UPLOAD_DIR=/data/uploads
 # 실제 접속 IP 전달을 검증한 후에만 활성화합니다.
 SAME_NETWORK_DISCOVERY_ENABLED=false
+LOCATION_DISCOVERY_ENABLED=true
+LOCATION_DISCOVERY_RADIUS_METERS=100
 TRUSTED_PROXY_CIDRS=
 CLIENT_IP_SOURCE=forwarded
 PROXY_DIAGNOSTIC_TOKEN=