[mob] Show face area info in debug mode

mobile/lib/face/model/detection.dart

@@ -43,6 +43,11 @@ class Detection {
     );
   }
 
+  // TODO: iterate on better area calculation, potentially using actual indexing image dimensions instead of file metadata
+  int getFaceArea(int imageWidth, int imageHeight) {
+    return (box.width * imageWidth * box.height * imageHeight).toInt();
+  }
+
   // TODO: iterate on better scoring logic, current is a placeholder
   int getVisibilityScore() {
     final double aspectRatio = box.width / box.height;

mobile/lib/ui/viewer/file_details/face_widget.dart

@@ -174,6 +174,12 @@ class _FaceWidgetState extends State<FaceWidget> {
                       style: Theme.of(context).textTheme.bodySmall,
                       maxLines: 1,
                     ),
+                  if (kDebugMode)
+                    Text(
+                      'A: ${widget.face.detection.getFaceArea(widget.file.width, widget.file.height)}',
+                      style: Theme.of(context).textTheme.bodySmall,
+                      maxLines: 1,
+                    ),
                   // if (kDebugMode)
                   //   if (highlight)
                   //     const Text(