feat: add Floor/Room models aligned with API

lib/domain/models/floor.dart

@@ -0,0 +1,51 @@
+class Floor {
+  const Floor({required this.id, required this.name});
+
+  final int id;
+  final String name;
+
+  factory Floor.fromJson(Map<String, dynamic> json) => Floor(
+        id: json['id'] as int,
+        name: json['name'] as String,
+      );
+}
+
+class Room {
+  const Room({
+    required this.id,
+    required this.name,
+    required this.floorId,
+    required this.x,
+    required this.y,
+    required this.width,
+    required this.height,
+  });
+
+  final int id;
+  final String name;
+  final int floorId;
+  final double x;      // offset from floor origin, meters
+  final double y;
+  final double width;  // meters
+  final double height; // meters
+
+  factory Room.fromJson(Map<String, dynamic> json) => Room(
+        id: json['id'] as int,
+        name: json['name'] as String,
+        floorId: json['floor_id'] as int,
+        x: ((json['x'] as num?) ?? 0).toDouble(),
+        y: (json['y'] as num? ?? 0).toDouble(),
+        width: (json['width'] as num).toDouble(),
+        height: (json['height'] as num).toDouble(),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'id': id,
+        'name': name,
+        'floor_id': floorId,
+        'x': x,
+        'y': y,
+        'width': width,
+        'height': height,
+      };
+}

lib/domain/models/tag.dart

@@ -47,8 +47,15 @@ class Tag {
 
 // Live position snapshot pushed from localiserd over Phoenix channel.
 class TagPosition {
-  const TagPosition({required this.tagId, required this.position});
+  const TagPosition({
+    required this.tagId,
+    required this.name,
+    required this.color,
+    this.roomId,
+  });
 
   final String tagId;
-  final Position position;
+  final String name;
+  final String color;  // hex color for chip rendering
+  final int? roomId;
 }