net: re-address hub network 10.60.1.0/24 -> 192.168.8.0/24

The project was designed around a 10.60.1.0/24 travel-router network,
but the actual RemoteRig router uses 192.168.8.0/24 (the C6 associates
and gets 192.168.8.x; hub confirmed at 192.168.8.56). Replace the
network prefix everywhere (last octet preserved; GoPro 10.5.5.1 left
alone).

- scripts/setup-pi.sh: static IP 192.168.8.56/24, gateway 192.168.8.1,
  deploy/health command examples updated
- esp32-mqtt-bridge.cpp: default mqtt_broker -> 192.168.8.56
- firmware/data/config.json: broker -> 192.168.8.56 (wifi_password kept
  blank in git; real value flashed to the device only)
- docs (CONTEXT, MQTT_CONTRACT, READMEs, wireframes): gateway/hub/DHCP
  and example IPs re-addressed for consistency

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

firmware/data/config.json

@@ -1,7 +1,7 @@
 {
   "wifi_ssid": "RemoteRig",
   "wifi_password": "",
-  "mqtt_broker": "10.60.1.56",
+  "mqtt_broker": "192.168.8.56",
   "mqtt_port": 1883,
   "camera_id": "",
   "heartbeat_interval_sec": 60,