Add Arch packaging and Forgejo workflows for bakery

- packaging/arch/PKGBUILD: builds the bakery CLI from the workspace
- .forgejo/workflows/package.yml: publishes to the [breadway] Arch registry on tag
- .forgejo/workflows/mirror.yml: mirrors to GitHub

.forgejo/workflows/package.yml

@@ -0,0 +1,40 @@
+name: Build and publish package
+
+on:
+  push:
+    tags: ['v*']
+
+jobs:
+  package:
+    runs-on: [self-hosted, hestia]
+    container:
+      image: archlinux:latest
+    steps:
+      # Note: no actions/checkout — the archlinux image has no Node, which JS
+      # actions require. Everything runs as shell steps and clones manually.
+      - name: Build and publish
+        env:
+          PUBLISH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          set -euo pipefail
+          VERSION="${GITHUB_REF_NAME#v}"
+          pacman -Syu --noconfirm base-devel git rust cargo
+          useradd -m builder
+          git config --global --add safe.directory '*'
+          git clone --branch "${GITHUB_REF_NAME}" --depth 1 \
+            "https://git.breadway.dev/${GITHUB_REPOSITORY}.git" /home/builder/src
+          cd /home/builder/src
+          git archive --format=tar.gz --prefix="bakery-${VERSION}/" HEAD \
+            > packaging/arch/bakery-${VERSION}.tar.gz
+          SHA=$(sha256sum packaging/arch/bakery-${VERSION}.tar.gz | awk '{print $1}')
+          sed -i "s/^pkgver=.*/pkgver=${VERSION}/" packaging/arch/PKGBUILD
+          sed -i "s/^sha256sums=.*/sha256sums=('${SHA}')/" packaging/arch/PKGBUILD
+          chown -R builder:builder /home/builder/src
+          # --nocheck: packaging builds the artifact; tests belong in a CI job.
+          su builder -c "cd /home/builder/src/packaging/arch && makepkg -f --noconfirm --nocheck"
+          PKG=$(find /home/builder/src/packaging/arch -name '*.pkg.tar.zst' | head -1)
+          curl -fsS -X PUT \
+            -H "Authorization: token ${PUBLISH_TOKEN}" \
+            -H "Content-Type: application/octet-stream" \
+            --data-binary "@${PKG}" \
+            "https://git.breadway.dev/api/packages/Breadway/arch/os"