Schema for object detection: double area + optional area

[jeffbl]

In the schema for Object Detection results, area is listed twice. Should be once.

In addition, "area" is listed as optional. However, when @gvzdv implemented object-detection-llm and did not include area:

1. sorting crashed since it assumes area is there
2. photo-audio-handler failed to render any objects since it also relied on area

If we require area, it should be required in schema. If we don't require it, downstream components should not crash, and do more reasonable things if it is missing.