feat(topology): track mesh node connections and render as map polylines

Add passive topology tracking from four sources with confidence ranking:
- Zero-hop MQTT observations (continuous, per-gateway, highest frequency)
- Traceroute replies (RouteDiscovery, full path + SNR data)
- NeighborInfo packets (self-reported neighbor SNR)
- relay_node inferred links (1-hop packets with known relay)

Backend: add rx_snr (field 62) and rx_rssi (field 63) to meshstream Data
proto; extract from MeshPacket in decoder.go; regenerate Go bindings.

Frontend:
- topologySlice: LinkObservation model, per-direction confidence merge,
  24h TTL pruning, 2000-edge cap, Redux-pure (timestamp from payload)
- aggregatorSlice: add hopsFromGateway to NodeData
- __root.tsx: dispatch processTopologyPacket after each SSE message
- NetworkMap: render polylines colored by SNR (green/yellow/red/gray),
  dimmed at 0.4 opacity for viaMqtt edges; Links toggle button in legend
- NodeDetail: Connections section showing per-edge SNR, source badge,
  viaMqtt badge, and last-seen time

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

decoder/decoder.go

@@ -112,6 +112,8 @@ func DecodeMessage(payload []byte, topicInfo *meshtreampb.TopicInfo) *meshtreamp
 	data.ViaMqtt = packet.GetViaMqtt()
 	data.NextHop = packet.GetNextHop()
 	data.RelayNode = packet.GetRelayNode()
+	data.RxSnr = packet.GetRxSnr()
+	data.RxRssi = packet.GetRxRssi()
 
 	// Process the payload
 	if packet.GetDecoded() != nil {