[S3-006] Decode original maps and mission information

Accidental duplicate of https://github.com/stacksjs/the-settlers-iii-remake/issues/22, created on 2026-10-22 when an interrupted roadmap publish (the disk filled during the run) could not see the existing issues. Closed without work; track S3-006 in https://github.com/stacksjs/the-settlers-iii-remake/issues/22.