修改输出文件编码为ANSI

将输出TXT文件的编码从UTF-8改为ANSI(Encoding.Default)
以确保与示例文件格式一致

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

FileMerger.cs

@@ -249,8 +249,8 @@ namespace SlideCombine
                     var outputFileName = $"{result.BaseFileName}.txt";
                     var outputFilePath = Path.Combine(outputPath, outputFileName);
 
-                    // 使用UTF-8编码保存
-                    File.WriteAllText(outputFilePath, result.OutputContent, Encoding.UTF8);
+                    // 使用ANSI编码保存 (Encoding.Default)
+                    File.WriteAllText(outputFilePath, result.OutputContent, Encoding.Default);
                 }
             }
         }