Publish an Arch package to the AUR from the release

The AppImage runs on Arch but not as a Wayland client. It carries Ubuntu's
GTK stack including libwayland-client, which cannot talk to a current
compositor, so on Hyprland it fails to initialise GTK and only starts once it
falls back to Xwayland. Verified both ways on a real session: the AppImage
comes up with xwayland 1, the packaged build with xwayland 0.

margin-calendar-bin repackages the published .deb rather than building from
source, which is forced rather than lazy. The Google OAuth client is embedded
at compile time from a file that is not in the repo, so a source package
would build cleanly on a stranger's machine and then tell them Google
Calendar is not set up.

The job runs after the manifest check, so the AUR can only ever point at a
release that survived it, and it checksums the artifact it just downloaded
rather than one it assumed was there. Without AUR_SSH_PRIVATE_KEY it renders
the package, warns, and leaves the release alone.

license=('custom') is honest rather than chosen: this repo has no licence
file. That is worth fixing before anyone else packages it.

packaging/aur/PKGBUILD.in

@@ -0,0 +1,32 @@
+# Maintainer: PJ <[email protected]>
+
+# The template the release workflow renders. @VERSION@ and @SHA256@ are filled in from the release
+# that has just published, so the PKGBUILD on the AUR always points at an artifact that exists.
+#
+# A binary package rather than one built from source, and that is forced rather than lazy: the
+# Google OAuth client is embedded at compile time from a file that is not in the repo, so anything
+# built from source on a stranger's machine runs and then says Google Calendar is not set up.
+
+pkgname=margin-calendar-bin
+pkgver=@VERSION@
+pkgrel=1
+pkgdesc="A calendar for Google Calendar, where the grid owns the window and the day fits without scrolling"
+arch=('x86_64')
+url="https://github.com/priyanshujain/margin-calendar"
+license=('custom')
+depends=('webkit2gtk-4.1' 'gtk3')
+provides=('margin-calendar')
+conflicts=('margin-calendar')
+# Prebuilt and already linked: stripping it again buys nothing and risks the binary.
+options=('!strip' '!debug')
+source=("${pkgname}-${pkgver}.deb::${url}/releases/download/v${pkgver}/Margin.Calendar_${pkgver}_amd64.deb")
+noextract=("${pkgname}-${pkgver}.deb")
+sha256sums=('@SHA256@')
+
+package() {
+    bsdtar -xOf "${pkgname}-${pkgver}.deb" data.tar.gz | bsdtar -xf - -C "${pkgdir}"
+    # The bundler names it after the product, spaces and all. Everything that reads this directory
+    # copes with that, and nothing that reads it enjoys it.
+    mv "${pkgdir}/usr/share/applications/Margin Calendar.desktop" \
+       "${pkgdir}/usr/share/applications/margin-calendar.desktop"
+}