feat: revamp sensor add flow

lib/domain/models/sensor.dart

@@ -2,6 +2,7 @@ class Sensor {
   const Sensor({
     required this.id,
     required this.sensorId,
+    required this.confirmed,
     this.name,
     this.roomId,
     this.x,
@@ -10,6 +11,7 @@ class Sensor {
 
   final int id;
   final String sensorId; // BLE MAC / provisioning device ID
+  final bool confirmed;  // true once seen on MQTT
   final String? name;    // human-readable label
   final int? roomId;
   final double? x;       // room relative
@@ -21,6 +23,7 @@ class Sensor {
   factory Sensor.fromJson(Map<String, dynamic> json) => Sensor(
         id: json['id'] as int,
         sensorId: json['sensor_id'] as String,
+        confirmed: json['confirmed'] as bool,
         name: json['name'] as String?,
         roomId: json['room_id'] as int?,
         x: (json['x'] as num?)?.toDouble(),
@@ -37,6 +40,7 @@ class Sensor {
       Sensor(
         id: id,
         sensorId: sensorId,
+        confirmed: confirmed,
         name: name ?? this.name,
         roomId: roomId ?? this.roomId,
         x: x ?? this.x,