Summary

Refactors and fixes the project save dialog (formerly FileDialog4Project).

Bug fix

Wrong variable in palette color logic: setValidProjectName() was using m_valid_project_path instead of m_valid_project_name, so the project name field never turned red when entering an invalid name (e.g., an existing directory name).

UX improvement

Initial validation: The dialog now validates the suggested project name immediately on open, showing a warning if the name already exists in the working directory. Previously, the user had to edit a field before any validation occurred.

Code quality

Renamed FileDialog4Project → SaveProjectDialog (more descriptive name)
Made setWorkingDirectory() private (internal use only)
Removed redundant nullptr initializations
Fixed typo "wether" → "whether"
Simplified QString("/") → "/"