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/src/esp32-mqtt-bridge.cpp

@@ -41,7 +41,7 @@
 struct Config {
   String wifi_ssid       = "RemoteRig";
   String wifi_password   = "";
-  String mqtt_broker     = "10.60.1.56";
+  String mqtt_broker     = "192.168.8.56";
   int    mqtt_port       = 1883;
   String camera_id       = "";   // assigned by hub
   int    heartbeat_sec   = 60;