v1.3.0

Adds GNU autotools support to the Atari ST toolkit Docker image and updates the installer-generated stcmd wrappers so the install-time Docker account/tag become the runtime defaults.

Changes:

Add autoconf, automake, libtool, and pkg-config to the Docker image via a new build stage.
Extend MiNT dependency install list (adds gemlib-m68k-atari-mint and pml-m68k-atari-mint).
Update Linux/Windows installers to embed install-time DOCKER_ACCOUNT and STCMD_IMAGE_TAG as defaults in the generated stcmd.