Switch the builder image to rust:1-bookworm — bevy's native linux
build needs glibc + alsa/udev, which does not build against musl —
and add the x86_64-pc-windows-gnu target with mingw-w64 for the
windows cross-compile (linker set from the Makefile, no per-repo
.cargo/config). Mac stays out: darwin needs osxcross, same as the
ebitengine mac plan. Builder steps pull the image on every run so
:latest updates reach the runner.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>