Refactor describe.py for primary/secondary region detection with bounding boxes
- Replace single "visible" category with primary/secondary regions, each with
category and normalized box_2d coordinates (0-1000 scale)
- Add image cropping for follow-up analysis based on bounding boxes
- Consolidate same-prompt-type follow-ups to use full frame instead of cropping
- Skip follow-ups for regions smaller than 300px in either dimension
- Upgrade all Gemini calls from GEMINI_LITE to GEMINI_FLASH
- Fix frame counting to only count initial requests, not follow-ups
- Add backward compatibility in screen formatter for legacy "visible" field
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>