feat: montly rebuilds of builder

.github/workflows/rebuild-builder.yml

@@ -0,0 +1,40 @@
+name: Rebuild Builder Image
+
+on:
+  workflow_dispatch: {} # For as needed rebuilds.
+  schedule:
+    - cron: "0 0 1 * *"
+
+jobs:
+  updater-base-image:
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+      contents: read
+    env:
+      REGISTRY: git.rgst.io
+      IMAGE_NAME: ${{ github.repository }}
+
+    steps:
+      - name: Checkout
+        uses: https://code.forgejo.org/actions/checkout@v4
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ github.token }}
+      - name: Use Last Commit Date as System Timestamp
+        run: echo "TIMESTAMP=$(git log -1 --pretty=%ct)" >> $GITHUB_ENV
+      - name: Build and push image
+        uses: docker/build-push-action@v6
+        id: push
+        env:
+          SOURCE_DATE_EPOCH: ${{ env.TIMESTAMP }}
+        with:
+          context: .
+          push: true
+          platforms: linux/amd64
+          tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}-builder