Support "Save with Encoding" Feature for Proper Encoding Conversion (Similar to VSCode)

[PKC278]

The app currently allows files to be reopened with a specific encoding by clicking on the encoding type in the bottom right corner (Reopen with Encoding). However, if the file is not in UTF-8, text in the terminal (e.g., Chinese) will appear garbled.

To improve this, it would be helpful to add a "Save with Encoding" feature to support encoding conversion, similar to how it's implemented in VSCode.