Reuse the established conventions rather than inventing new ones: the
AUR_SSH_PRIVATE_KEY secret name, pushing from an archlinux:base-devel
job container instead of docker-in-docker, and the existing git identity.
The AUR job only needs the PKGBUILD, so the 1.5 GB tarball never crosses
a job boundary - it goes straight to GitHub Releases from the build job.
Also correct the Gitea job-timeout setting name to ENDLESS_TASK_TIMEOUT.
Upstream JASP ships no Linux binary, so the existing AUR package builds
everything from source including several hundred R packages. This builds
that once in CI and publishes the result as jasp-desktop-bin.
JASP links against the system R and Qt6 rather than bundling them, so a
rebuild is triggered by an Arch r/qt6-base bump as well as by a new JASP
release, and the generated PKGBUILD pins depends to the versions actually
built against.