CI: fix Arch-registry publish (use makepkg --packagelist; !strip for cross-arch repack)

The runner's PKGEXT is .pkg.tar.xz, so the .zst glob never matched;
--packagelist yields the exact filename, and options=('!strip') lets the
foreign-arch binary be packaged on the aarch64 host without stripping.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GLUwWE2KmFPzhKaf67tWbx

aur/PKGBUILD

@@ -4,6 +4,7 @@ pkgver=0.1.3
 pkgrel=1
 pkgdesc="Wayland layer-surface wallpaper runner powered by GLSL/WGSL fragment shaders (wgpu)"
 arch=('x86_64' 'aarch64')
+options=('!strip')
 url="https://project.uhhm.no/bl/gpupaper"
 license=('MIT')
 depends=('wayland' 'libglvnd')