Dockerfile — Reproducible Build Environment

• Base: ubuntu:22.04
• Installs build-essential, git, wget, python3, genisoimage
• Installs KOS deps: libpng-dev, libjpeg-dev, zlib1g-dev, libelf-dev
• Installs gcc-sh4-linux-gnu cross-compiler
• Sets KOS_BASE=/opt/toolchains/dc/kos, clones KallistiOS from GitHub
• Defines WORKDIR /workspace, copies scripts to /usr/local/bin/