Audacity 4 on Windows cannot open AUP3 files with Japanese characters in the filename

### Bug description

Audacity 4 fails to open an existing .aup3 project when the filename contains Japanese characters.

The Japanese characters in the filename/path are displayed as garbled characters in the error dialog.

If I rename exactly the same .aup3 file using only ASCII characters, Audacity 4 opens and converts it successfully.

### Steps to reproduce

On Windows 11, prepare an existing Audacity .aup3 project.
Give the file a name containing Japanese characters, for example 録音テスト.aup3.
Open the file in Audacity 4.
Audacity reports that the file cannot be found/opened, and the Japanese characters in the path are garbled.
Rename the same file to test.aup3.
Open it again.
The project opens successfully.

### Expected behavior

Audacity should correctly handle Unicode/Japanese characters in project filenames and paths.

### Actual behavior

Japanese characters in the path appear to be incorrectly encoded, and Audacity cannot locate/open the project.

### Audacity Version

Audacity 4.0.0

### Operating system

Windows

### Additional context

The .aup3 project itself does not appear to be corrupted, because simply renaming the file to an ASCII-only filename allows Audacity 4 to open it successfully.

I have attached a screenshot of the error dialog showing the garbled Japanese filename.

Start by reproducing the failure on Windows 11 with the attached Japanese-named .aup3 project, then compare project opening and error-path handling with the ASCII filename case. Done means Audacity opens existing .aup3 files with Japanese characters and displays their paths without garbling.

Written by the indexing model from the issue text.