Clean up stray files and expand test coverage for char/empty-string comparison fix

Remove leftover patch artifacts (.orig, .rej, patch file) and temporary TestDotNet
debugging files that were committed by mistake. Expand the regression test to also
cover the not-equal (<>) operator case.

https://claude.ai/code/session_01AkwUvu3XuCdj3D4axoX4UX

Author: claude

CodeConverter/CSharp/BinaryExpressionConverter.cs.orig

@@ -552,6 +552,7 @@ Private Sub TestMethod()
         Dim testChar As Char = Nothing
         Dim testResult = testChar = """"
         Dim testResult2 = """" = testChar
+        Dim testResult3 = testChar <> """"
     End Sub
 End Class", @"
 internal partial class TestClass
@@ -561,6 +562,7 @@ private void TestMethod()
         char testChar = default;
         bool testResult = testChar == char.MinValue;
         bool testResult2 = char.MinValue == testChar;
+        bool testResult3 = testChar != char.MinValue;
     }
 }");
     }