Wire subnet discovery routes and relay scan UDP hints.

Register recon history/export/canary APIs and discovered-hosts on the router; map UDP and path-tracer hints in relay ToScanReport; wire public canary ping to ReconHandler.

server/internal/recon/relay_scan.go

@@ -138,6 +138,7 @@ func (r *RelayScanReport) ToScanReport() *ScanReport {
 	}
 	return &ScanReport{
 		Host: r.Host, ScannedAt: r.ScannedAt, Ports: r.Ports, RelayVia: relayVia,
+		UDPHints: r.UDPHints, PathTracerHints: r.PathTracerHints,
 		Recommendations: r.Recommendations,
 	}
 }