Drop pacman packaging, bakery-only distribution

bakery already fully covers what the PKGBUILD provided (binary, systemd
--user service where applicable, dependency declarations) except a LICENSE
copy, which bakery.toml's new license_file field now closes. Removes
packaging/arch/ and .forgejo/workflows/package.yml; adds the LICENSE
artifact to each release/dev-release/beta-release workflow's prepare
step. Not pacman-installed inside BOS today (BOS already consumes these
apps exclusively via build-local.sh's skel-staging), so this only removes
the option to `pacman -S` outside of BOS/bakery.

packaging/arch/PKGBUILD

@@ -1,34 +0,0 @@
-# Maintainer: Breadway <rileyhorsham@gmail.com>
-
-pkgname=breadpaper
-pkgver=0.1.0
-pkgrel=1
-pkgdesc="Wallpaper manager for the bread desktop"
-arch=('x86_64')
-url="https://github.com/Breadway/breadpaper"
-license=('MIT')
-options=(!lto !debug)
-depends=('glibc')
-optdepends=(
-  'python-pywal: colour palette generation from wallpaper (AUR)'
-  'awww: Wayland wallpaper daemon'
-)
-makedepends=('rust' 'cargo')
-source=("${pkgname}-${pkgver}.tar.gz")
-sha256sums=('SKIP')
-
-build() {
-  cd "${srcdir}/${pkgname}-${pkgver}"
-  cargo build --release --locked
-}
-
-check() {
-  cd "${srcdir}/${pkgname}-${pkgver}"
-  cargo test --release --locked
-}
-
-package() {
-  cd "${srcdir}/${pkgname}-${pkgver}"
-  install -Dm755 target/release/breadpaper "${pkgdir}/usr/bin/breadpaper"
-  install -Dm644 LICENSE "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE"
-}