feat: implement sensor calibration flow

lib/data/sources/localiser/realtime_data_client.dart

@@ -78,6 +78,12 @@ class RealtimeDataClient {
         .map((msg) => (event: msg.event.value, payload: msg.payload ?? const {}));
   }
 
+  /// Leaves [topic] and removes it from the channel cache.
+  void leaveChannel(String topic) {
+    final ch = _channels.remove(topic);
+    ch?.leave();
+  }
+
   /// Pushes [event] on [topic] and waits for the server reply.
   /// The channel must have been joined first via [channel].
   Future<Map<String, dynamic>> push(

lib/data/sources/localiser/sensor_client.dart

@@ -38,17 +38,22 @@ class SensorClient extends LocaliserdClient {
           })
           as Map<String, dynamic>;
 
-  Future<Map<String, dynamic>> startCalibration(
-    int id,
-    double referenceDistance,
-  ) async =>
-      await post('/api/sensors/$id/calibration/start', {
-            'reference_distance': referenceDistance,
+  Future<Map<String, dynamic>> beginCalibration(int id) async =>
+      await post('/api/sensors/$id/calibration/begin') as Map<String, dynamic>;
+
+  Future<Map<String, dynamic>> startStage(int id, double distance) async =>
+      await post('/api/sensors/$id/calibration/stage', {
+            'distance': distance,
           })
           as Map<String, dynamic>;
 
-  Future<Map<String, dynamic>> stopCalibration(int id) async =>
-      await post('/api/sensors/$id/calibration/stop') as Map<String, dynamic>;
+  Future<Map<String, dynamic>> finishCalibration(int id) async =>
+      await post(
+        '/api/sensors/$id/calibration/finish',
+      ) as Map<String, dynamic>;
+
+  Future<void> cancelCalibration(int id) =>
+      delete('/api/sensors/$id/calibration');
 
   Future<String> getVersion(int id) async {
     final response =