chore(sonar): remove three unused local variables (S1481)

- LinqQueryBreakdown.cs:211 - drop unused `expr` pattern binding (type test remains)
- LinqQueryBreakdown.cs:279 - drop unused `firstEntity` (empty check already above)
- LinqExpressionVisitor.cs:315 - drop unused `param` pattern binding

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Strata.SqlTools.LinqToSql/Breakdowns/LinqQueryBreakdown.cs

@@ -208,7 +208,7 @@ public class LinqQueryBreakdown : QueryBreakdown
         {
             // If the original expression can be converted to IQueryable<T>, use it
             // Otherwise, we cannot safely reconstruct without the original query provider
-            if (OriginalExpression is Expression expr && EntityType == typeof(T))
+            if (OriginalExpression is Expression && EntityType == typeof(T))
             {
                 // We have the expression, but we don't have the provider to create IQueryable<T>
                 // The breakdown analysis is one-way; reconstruction requires the original provider
@@ -275,8 +275,7 @@ public class LinqQueryBreakdown : QueryBreakdown
         var breakdown = new Breakdowns.SqlServer.InsertBreakdown();
         breakdown.TableName.Clause = typeof(T).Name;
 
-        // Use first entity to get column names
-        var firstEntity = entitiesList.First();
+        // Use the entity type to get column names
         var properties = typeof(T).GetProperties();
         var columnNames = new List<string>();
 

src/Strata.SqlTools.LinqToSql/Visitors/LinqExpressionVisitor.cs

@@ -312,7 +312,7 @@ public class LinqExpressionVisitor : ExpressionVisitor
             return GetFullMemberName(member);
         }
 
-        if (expression is ParameterExpression param)
+        if (expression is ParameterExpression)
         {
             return "*";
         }