Drop pacman packaging, bakery-only distribution

bakery already fully covers what the PKGBUILD provided (binary, 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.

.forgejo/workflows/dev-release.yml

@@ -53,6 +53,7 @@ jobs:
           strip "${PKG_DIR}/breadbar-x86_64"
           sha256sum "${PKG_DIR}/breadbar-x86_64" | awk '{print $1}' \
             > "${PKG_DIR}/breadbar-x86_64.sha256"
+          cp src/LICENSE "${PKG_DIR}/"
           cp src/bakery.toml "${PKG_DIR}/bakery.toml"
           ln -sfn "${VERSION}" "/srv/breadway-dl/dev/breadbar/latest"