let segmentation honour its post-processing configuration

Segmentation reuses the detection suppressor but passed only the IoU threshold,
so it silently fell back to the hardcoded containment constant while detection
had just been given a configured one. Tuning containment for a promoted model
would have changed detection behaviour and left segmentation on the old value —
the same drift, one commit later.

Masks and boxes overlap differently, so segmentation carries its own setting
rather than borrowing the detector's, and records both thresholds on the run as
detection does.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.env.example

@@ -143,6 +143,9 @@ YOLO_SUPPRESS_TILE_EDGE_DETECTIONS=true
 # Serving a promoted model at a different value means the runtime suppresses
 # detections its gate counted, so set this to the value the candidate was gated at.
 YOLO_CONTAINMENT_NMS_THRESHOLD=0.85
+# Segmentation carries its own value: masks and boxes overlap differently,
+# so one threshold need not fit both.
+SEGMENTATION_CONTAINMENT_NMS_THRESHOLD=0.85
 
 # Local segmentation models. GeoIntel never downloads model weights
 # automatically; point these to existing local files to enable inference.