Fix skip-existing logic for batch import duplicates

The skipUpdate flag should only apply to existing DB issues, not to
duplicates within the import batch. Batch duplicates always use
last-one-wins semantics.

cmd/bd/import.go

@@ -254,10 +254,7 @@ Behavior:
 
 		 // Handle duplicates within the same import batch (last one wins)
 		 if idx, ok := seenNew[issue.ID]; ok {
-				if skipUpdate {
-		    skipped++
-		    continue
-				}
+		 // Last one wins regardless of skipUpdate (skipUpdate only applies to existing DB issues)
 		 newIssues[idx] = issue
 		 } else {
 		 seenNew[issue.ID] = len(newIssues)