make all header file responses ascii compliant

Controllers/ResponseEnricher.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using System.Text;
 using System.Xml;
 using System.Xml.Serialization;
@@ -9,11 +10,44 @@ namespace NejCommon.Controllers;
 
 public static class Responses
 {
+    public static string ToAscii(string input)
+    {
+        if (string.IsNullOrEmpty(input))
+            return input;
+
+        // Normalize to FormD (decomposition)
+        string normalized = input.Normalize(NormalizationForm.FormD);
+
+        var sb = new StringBuilder();
+
+        foreach (char c in normalized)
+        {
+            var unicodeCategory = CharUnicodeInfo.GetUnicodeCategory(c);
+            // Skip non-spacing marks (accents, umlauts, etc.)
+            if (unicodeCategory != UnicodeCategory.NonSpacingMark)
+            {
+                sb.Append(c);
+            }
+        }
+
+        // Normalize back to FormC and remove any remaining non-ASCII chars
+        string cleaned = sb.ToString().Normalize(NormalizationForm.FormC);
+
+        // Ensure only ASCII characters remain
+        var ascii = new StringBuilder();
+        foreach (char c in cleaned)
+        {
+            ascii.Append(c <= 127 ? c : '?'); // replace non-ASCII with '?' or remove
+        }
+
+        return ascii.ToString();
+    }
+
     public static FileStreamHttpResult RespondFileStream(this ControllerBase controller, Stream stream, string contentType, string fileName)
     {
         stream.Seek(0, SeekOrigin.Begin);
 
-        controller.Response.Headers.Add("Content-Disposition", "inline; filename=" + fileName);
+        controller.Response.Headers.Add("Content-Disposition", "inline; filename=" + ToAscii(fileName.Normalize(NormalizationForm.FormD)));
         return TypedResults.File(stream, contentType, fileName);
     }
     public static FileStreamHttpResult RespondXlsx(this ControllerBase controller, XLWorkbook file, string fileName)