New /config/zone page lets users draw a polygon over a camera frame
(including live RTSP snapshot) to define the area where vehicle detection
applies. Zone is stored in /data/zone.json and applied in two ways:
- Motion scoring: inter-frame diff is masked outside the zone so garden
movement doesn't inflate frame scores
- YOLO plate detection: detections whose center falls outside the zone
are filtered out
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
