feat: include self-reported tx_power in measurement calls

lib/localiser/localisation/sensor/server.ex

@@ -21,9 +21,10 @@ defmodule Localiser.Localisation.Sensor.Server do
     {:via, Registry, {Localiser.Registry, {:sensor, sensor_id}}}
   end
 
-  # Returns %{sensor_id, floor_x, floor_y, distance} for a raw RSSI reading.
-  def measure(sensor_id, rssi) do
-    GenServer.call(via(sensor_id), {:measure, rssi})
+  # Returns %{sensor_id, floor_x, floor_y, distance, rssi, tx_power} for a raw RSSI reading.
+  # tx_power is the beacon-advertised expected RSSI at 1 m (nil if not available).
+  def measure(sensor_id, rssi, tx_power \\ nil) do
+    GenServer.call(via(sensor_id), {:measure, rssi, tx_power})
   end
 
   # Returns true if the sensor is currently collecting calibration samples.
@@ -66,14 +67,16 @@ defmodule Localiser.Localisation.Sensor.Server do
   end
 
   @impl true
-  def handle_call({:measure, rssi}, _from, state) do
+  def handle_call({:measure, rssi, tx_power}, _from, state) do
     distance = rssi_to_distance(rssi, state.rssi_ref, state.path_loss_exp)
 
     measurement = %{
       sensor_id: state.sensor_id,
       floor_x: state.floor_x,
       floor_y: state.floor_y,
-      distance: distance
+      distance: distance,
+      rssi: rssi,
+      tx_power: tx_power
     }
 
     {:reply, measurement, state}