S7: Adopt and replace sensor nodes

[xishell]

Persona

Harbor master + Harbor maintenance

User outcome

As a harbormaster, I would like to be able to adopt new nodes into the system, so that I can perform maintenance.

Sensor hardware will fail or need replacement. The provisioning flow must be usable by non-technical staff with a tablet.

Acceptance Criteria

• Harbor master can provision a new node by scanning a QR code and picking a berth
• A failed node can be replaced without modifying backend configuration
• Full provisioning completes in under 60 seconds for a non-technical user
• Provisioned nodes survive reboot without re-pairing