give segmentation QA the same threshold-independent view as detection

Detection QA reports a precision/recall curve, average precision and a
calibration sweep; segmentation QA reported a single operating point. Both rank
their outputs by confidence, so the same view applies, and the asymmetry meant
the two panels answered different questions about comparable runs — an
inconsistency introduced when detection gained the curve.

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

frontend/src/types.ts

@@ -1620,6 +1620,8 @@ export interface SegmentationQaRequest {
   iou_threshold: number
   class_name?: string | null
   min_confidence?: number | null
+  /** Read off the one matching pass, exactly as for detection. */
+  calibration_thresholds?: number[]
 }
 
 export type SegmentationQaResult = DetectionQaResult