Make Forgejo workflow node-free (manual git checkout)

The mac-mini runner runs jobs in host mode with no Node, so JS actions
like actions/checkout fail with 'Cannot find: node in PATH'. Replace it
with a plain git init/fetch/checkout so the workflow needs only git +
docker, both present on the host.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.forgejo/workflows/docker-build.yml

@@ -8,12 +8,16 @@ jobs:
   build-and-push:
     runs-on: ubuntu-latest
     steps:
+      # Manual checkout with plain git — the runner has no Node, so JS actions
+      # like actions/checkout can't run. git + docker are available on the host.
       - name: Checkout
-        uses: actions/checkout@v4
+        run: |
+          git init -q .
+          git remote add origin "https://${{ github.actor }}:${{ secrets.GITHUB_TOKEN }}@git.plexultra.com/${{ github.repository }}.git" \
+            || git remote set-url origin "https://${{ github.actor }}:${{ secrets.GITHUB_TOKEN }}@git.plexultra.com/${{ github.repository }}.git"
+          git fetch --depth 1 origin "${{ github.ref_name }}"
+          git checkout -q -f FETCH_HEAD
 
-      # Forgejo's built-in container registry. The auto-provided token can push
-      # packages for the repo owner; if push fails on auth, create a Forgejo
-      # access token with package read/write and use it here instead.
       - name: Log in to Forgejo container registry
         run: echo "${{ secrets.GITHUB_TOKEN }}" | docker login git.plexultra.com -u "${{ github.actor }}" --password-stdin