CI: build and use specific container image

.forgejo/Containerfile.build

@@ -0,0 +1,6 @@
+# Containerfile for CI build container
+
+FROM archlinux:base-devel
+
+RUN pacman -Sy --noconfirm archlinux-keyring && pacman -Syu --noconfirm nodejs git openssh hugo go git-lfs rsync just markdownlint-cli2 clang
+RUN git lfs install

.forgejo/workflows/build-builder.yml

@@ -0,0 +1,18 @@
+on:
+  workflow_dispatch:
+  schedule:
+    cron: "0 17 * * 2" # every monday evening
+
+jobs:
+  build_and_push:
+    name: Build and push container
+    runs-on: archlinux
+    steps:
+      - name: Login to registry
+        run: echo ${{ secrets.CONTAINER_REGISTRY_PASS }} | docker login -u ${{ vars.CONTAINER_REGISTRY_USER }} --password-stdin git.it-syndikat.org
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          file: .forgejo/Containerfile.build
+          push: true
+          tags: ${{ vars.BUILDER_CONTAINER_NAME }}

.forgejo/workflows/deploy.yml

@@ -5,16 +5,10 @@ jobs:
   build:
     runs-on: docker
     container:
-      image: archlinux:base-devel
+      image: ${{ vars.BUILDER_CONTAINER_NAME }}
     env:
       HUGO_CACHEDIR: /tmp/hugo_cache
     steps:
-      - name: Prepare container
-        run: |
-          pacman -Sy --noconfirm archlinux-keyring
-          pacman -Syu --noconfirm
-          pacman -S --noconfirm nodejs git make pacman-contrib base base-devel openssh wget curl procps-ng bash hugo go git-lfs rsync just markdownlint-cli2 clang
-          git lfs install
       - name: Checkout
         uses: actions/checkout@v4
         with: