docs(ota_demo): add architecture diagram to README

demos/ota_nav2_sensor_fix/README.md

@@ -4,6 +4,15 @@ End-to-end demo: a `ros2_medkit` gateway with a dev-grade OTA plugin that
 demonstrates a real update / publish-a-hotfix loop on a ROS 2 node without
 SSH-ing into the robot.
 
+## Architecture
+
+Off-board tooling drives the on-board robot over one SOVD REST API: the gateway
+registers and applies OTA updates (the OTA Update Agent hot-swaps the lidar
+node), while the fault bridges and the Fault Manager turn Nav2's own failures
+into SOVD faults.
+
+![OTA over SOVD - nav2 sensor-fix demo architecture](docs/architecture.svg)
+
 ## What this shows
 
 The headline scene is a diagnostic loop, not just a button-press update:
@@ -168,7 +177,7 @@ curl -X DELETE "${API}/apps/controller-server/faults"
 # 8. Resume the mission (or use ./send-goal.sh).
 ```
 
-## Foxglove Studio visualization
+## Foxglove visualization
 
 The gateway container bakes in a Robotnik RB-Theron AMR + Nav2 stack running
 on top of headless Gazebo in the AWS small-warehouse world. `foxglove_bridge`
@@ -177,7 +186,7 @@ runs on port `8765` and exposes the full topic set: `/tf`, `/tf_static`,
 `/local_costmap/costmap`, etc. - so a Foxglove **3D** panel renders the actual
 robot in the warehouse out of the box.
 
-1. Open Foxglove Studio -> **Open connection** -> **Foxglove WebSocket** ->
+1. Open Foxglove -> **Open connection** -> **Foxglove WebSocket** ->
    `ws://localhost:8765`. The Topics panel should list all of the topics
    above.
 2. Drop in a **3D** panel. In its settings set **Scene -> Mesh up axis ->

demos/ota_nav2_sensor_fix/ros2_packages/ota_nav2_sensor_fix_demo/launch/demo.launch.py

@@ -8,7 +8,7 @@
 #   - the Robotnik RB-Theron AMR spawned in that world, driven through
 #     gz_ros2_control + a stock diff_drive_controller
 #   - the full Nav2 stack (bringup_launch.py) with the warehouse map
-#   - foxglove_bridge on :8765 so Foxglove Studio can render /tf, /scan, /map etc.
+#   - foxglove_bridge on :8765 so Foxglove can render /tf, /scan, /map etc.
 #   - ros2_medkit fault_manager (the gateway's /faults endpoint depends on it)
 #   - the gateway with our ota_update_plugin loaded via gateway_config.yaml
 #   - ros2_medkit_log_bridge + ros2_medkit_action_status_bridge, started

demos/ota_nav2_sensor_fix/run-demo.sh

@@ -201,7 +201,7 @@ echo "  Web UI (ros2_medkit_web_ui):"
 echo "    npm install && npm run dev"
 echo "    open http://localhost:5173 -> Connect -> ${GATEWAY_URL}"
 echo ""
-echo "  Foxglove Studio (recommended for the 3D narrative):"
+echo "  Foxglove (recommended for the 3D narrative):"
 echo "    Open connection -> Foxglove WebSocket -> ws://localhost:${OTA_FOXGLOVE_BRIDGE_PORT:-8765}"
 echo "    Add a 3D panel: TurtleBot3 in the world, /scan cone shows the phantom"
 echo "    Install ros2_medkit_foxglove_extension (npm run local-install) for the"