Fix issues 163, 164, and 165

[DiyunZ]

This PR fixes three issues found while testing the LASSIE-to-CMOD workflow:

• Preserve the project seed when opening and saving.
• Reject malformed or incomplete project XML without replacing the current project.
• Correctly handle Windows paths and report audio-writing failures as failed builds.
  Verified with a full build, all local tests, and a successful CMOD audio render.

Fixes #163
Fixes #164
Fixes #165