[bug]: gbk格式txt文件预览乱码

[wudeh]

Summary

1.txt

Reproduction

1

Environment

Windows 11 专业版，25H2，26200.8875；

Console or network errors

[wybaby168]

Reproduced with the attached 4-byte file: b2 e2 ca d4 is invalid UTF-8 and decodes as GBK/GB18030 to 测试. The current normal and virtual text paths both assume UTF-8, so this is a valid renderer bug. We will fix both paths with UTF-8-first/GB18030 auto detection plus an explicit encoding override, and add a regression for these bytes. Thanks.