Upgrade async GPU analysis and workbench UX

backend/app/schemas/segmentation.py

@@ -102,4 +102,9 @@ class SegmentationRead(BaseModel):
 
 class SegmentationListResponse(BaseModel):
     items: list[SegmentationRead]
+    # ``total`` describes the complete filtered population; ``items`` is one
+    # stable confidence-ranked page of it.
     total: int
+    limit: int | None = None
+    offset: int = 0
+    truncated: bool = False