Fix CI: replace actions/checkout with git clone (no Node.js needed)

Host-mode runner has no Node.js so JS composite actions fail.
All steps are now plain shell — git clone for checkout, docker
CLI for build/push. Zero external action dependencies.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/docker.yml

@@ -16,7 +16,11 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        run: |
+          git clone --depth 1 \
+            https://${{ github.actor }}:${{ secrets.GITHUB_TOKEN }}@git.hexadual.io/${{ github.repository }}.git \
+            .
+          git checkout ${{ github.sha }}
 
       - name: Log in to registry
         run: |
@@ -43,4 +47,4 @@ jobs:
 
       - name: Logout
         if: always()
-        run: docker logout ${{ env.REGISTRY }}
+        run: docker logout ${{ env.REGISTRY }} || true