feat: advance legacy UI behavior parity

src/MBN_STOCK_WEBVIEW.LegacyApplication/Comparison/LegacyComparisonWorkflowController.cs

@@ -333,17 +333,6 @@ public sealed class LegacyComparisonWorkflowController
             throw new InvalidOperationException("The saved comparison pair limit was reached.");
         }
 
-        var signature = LegacyComparisonWorkflowCatalog.PairSignature(
-            _firstTarget,
-            _secondTarget);
-        if (_savedPairs.Any(pair => string.Equals(
-                LegacyComparisonWorkflowCatalog.PairSignature(pair.First, pair.Second),
-                signature,
-                StringComparison.Ordinal)))
-        {
-            throw new InvalidOperationException("The exact comparison pair is already saved.");
-        }
-
         var rowId = $"comparison-pair-{++_pairSequence:D8}";
         var candidate = new List<SavedPairState>(_savedPairs)
         {