feat: add tag picker in sensor calibration flow

lib/features/sensors/calibration_notifier.dart

@@ -25,22 +25,22 @@ class CalibrationNotifier extends StateNotifier<CalibrationState> {
   /// Channel subscription is set up first to guarantee no reading events are
   /// dropped before the server acknowledges the stage start.
   Future<void> beginCalibration() async {
-    // Subscribe first, then call REST.
     _sub = repo
         .calibrationEvents(sensorDeviceId)
         .listen(_onEvent, onError: _onError);
 
     try {
       final samplesNeeded = await repo.beginCalibration(sensorId);
-      final firstUncompleted = calibrationDistances.first;
       state = state.copyWith(
-        phase: CalibrationPhase.ready,
+        phase: CalibrationPhase.selectingTag,
         samplesNeeded: samplesNeeded,
         samplesCollected: 0,
-        selectedDistance: firstUncompleted,
+        selectedDistance: calibrationDistances.first,
         completedDistances: {},
         waveform: [],
         clearLatestRssi: true,
+        clearTagRssiReadings: true,
+        clearSelectedTagId: true,
       );
     } catch (e) {
       _sub?.cancel();
@@ -52,6 +52,28 @@ class CalibrationNotifier extends StateNotifier<CalibrationState> {
     }
   }
 
+  void selectTag(String tagId) {
+    if (state.phase != CalibrationPhase.selectingTag) return;
+    state = state.copyWith(selectedTagId: tagId);
+  }
+
+  Future<void> commitTag() async {
+    final tagId = state.selectedTagId;
+    if (tagId == null || state.phase != CalibrationPhase.selectingTag) return;
+    try {
+      final samplesNeeded = await repo.setCalibrationTag(sensorId, tagId);
+      state = state.copyWith(
+        phase: CalibrationPhase.ready,
+        samplesNeeded: samplesNeeded,
+      );
+    } catch (e) {
+      state = state.copyWith(
+        phase: CalibrationPhase.error,
+        error: e.toString(),
+      );
+    }
+  }
+
   void selectDistance(double distance) {
     if (state.phase != CalibrationPhase.ready) return;
     if (state.completedDistances.contains(distance)) return;
@@ -111,6 +133,11 @@ class CalibrationNotifier extends StateNotifier<CalibrationState> {
 
   void _onEvent(({String event, Map<String, dynamic> payload}) msg) {
     switch (msg.event) {
+      case 'scan_reading':
+        _handleScanReading(msg.payload);
+      case 'tag_set':
+        final tagId = msg.payload['tag_id'] as String;
+        state = state.copyWith(selectedTagId: tagId);
       case 'reading':
         _handleReading(msg.payload);
       case 'stage_complete':
@@ -122,6 +149,14 @@ class CalibrationNotifier extends StateNotifier<CalibrationState> {
     }
   }
 
+  void _handleScanReading(Map<String, dynamic> payload) {
+    final tagId = payload['tag_id'] as String;
+    final rssi = (payload['rssi'] as num).toDouble();
+    state = state.copyWith(
+      tagRssiReadings: {...state.tagRssiReadings, tagId: rssi},
+    );
+  }
+
   void _handleReading(Map<String, dynamic> payload) {
     final rssi = (payload['rssi'] as num).toDouble();
     final progress = payload['stage_progress'] as Map<String, dynamic>;