feat: align Sensor model with API

lib/domain/models/sensor.dart

@@ -1,56 +1,49 @@
-import 'position.dart';
-
-enum SensorStatus { online, offline, provisioning }
-
 class Sensor {
   const Sensor({
     required this.id,
-    required this.name,
-    required this.floorId,
-    required this.position,
-    required this.status,
-    this.lastSeen,
+    required this.sensorId,
+    this.name,
+    this.roomId,
+    this.x,
+    this.y,
+    this.rssiRef,
   });
 
-  final String id;
-  final String name;
-  final String floorId;
-  final Position position;
-  final SensorStatus status;
-  final DateTime? lastSeen;
+  final int id;
+  final String sensorId; // BLE MAC / provisioning device ID
+  final String? name;    // human-readable label
+  final int? roomId;
+  final double? x;       // floor_x from API
+  final double? y;       // floor_y from API
+  final double? rssiRef;
+
+  bool get isPlaced => roomId != null;
+  String get displayName => name ?? sensorId;
+
+  factory Sensor.fromJson(Map<String, dynamic> json) => Sensor(
+        id: json['id'] as int,
+        sensorId: json['sensor_id'] as String,
+        name: json['name'] as String?,
+        roomId: json['room_id'] as int?,
+        x: (json['floor_x'] as num?)?.toDouble(),
+        y: (json['floor_y'] as num?)?.toDouble(),
+        rssiRef: (json['rssi_ref'] as num?)?.toDouble(),
+      );
 
   Sensor copyWith({
     String? name,
-    Position? position,
-    SensorStatus? status,
-    DateTime? lastSeen,
+    int? roomId,
+    double? x,
+    double? y,
+    double? rssiRef,
   }) =>
       Sensor(
         id: id,
+        sensorId: sensorId,
         name: name ?? this.name,
-        floorId: floorId,
-        position: position ?? this.position,
-        status: status ?? this.status,
-        lastSeen: lastSeen ?? this.lastSeen,
-      );
-
-  Map<String, dynamic> toJson() => {
-        'id': id,
-        'name': name,
-        'floor_id': floorId,
-        'position': position.toJson(),
-        'status': status.name,
-        'last_seen': lastSeen?.toIso8601String(),
-      };
-
-  factory Sensor.fromJson(Map<String, dynamic> json) => Sensor(
-        id: json['id'] as String,
-        name: json['name'] as String,
-        floorId: json['floor_id'] as String,
-        position: Position.fromJson(json['position'] as Map<String, dynamic>),
-        status: SensorStatus.values.byName(json['status'] as String),
-        lastSeen: json['last_seen'] == null
-            ? null
-            : DateTime.parse(json['last_seen'] as String),
+        roomId: roomId ?? this.roomId,
+        x: x ?? this.x,
+        y: y ?? this.y,
+        rssiRef: rssiRef ?? this.rssiRef,
       );
 }