Fix IndexError in grounding_parser.py for 2-coordinate bounding boxes

[atheendre130505]

• Handle both 2-coordinate points [x,y] and 4-coordinate boxes [x1,y1,x2,y2]
• Convert 2-coordinate points to small bounding boxes around the point
• Add validation to skip invalid coordinate formats with warnings
• Fix IndexError: list index out of range when model outputs 2 coordinates
• Maintain backward compatibility with existing 4-coordinate functionality

Resolves grounding coordinate parsing issues in GUI agent tasks