ci: add deploy workflow — retag SHA as latest on main merge

deploy.yaml (main push only):
  - Pull image by SHA tag (already pushed during PR CI)
  - Tag as :latest and push
  - No rebuild needed

.gitea/workflows/deploy.yaml

@@ -0,0 +1,44 @@
+name: Deploy
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+env:
+  REGISTRY: forgejo.riotpiao.com
+  IMAGE: forgejo.riotpiao.com/riotpiao-poimen/poimen-memory
+  DOCKER_HOST: tcp://localhost:2375
+
+jobs:
+  deploy:
+    name: Tag & Push Latest
+    runs-on: rust
+    steps:
+      - name: Install Docker
+        run: apt-get update && apt-get install -y docker.io
+
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Get short SHA
+        id: sha
+        run: echo "short_sha=$(git rev-parse --short HEAD)" >> $GITHUB_OUTPUT
+
+      - name: Registry login
+        run: |
+          echo "${REGISTRY_TOKEN}" | docker login "${REGISTRY}" \
+            --username "${REGISTRY_USER}" --password-stdin
+        env:
+          REGISTRY_USER: ${{ secrets.FORGEJO_REGISTRY_USER }}
+          REGISTRY_TOKEN: ${{ secrets.FORGEJO_REGISTRY_TOKEN }}
+
+      - name: Pull SHA image and tag as latest
+        run: |
+          docker pull "${IMAGE}:${{ steps.sha.outputs.short_sha }}" && \
+          docker tag "${IMAGE}:${{ steps.sha.outputs.short_sha }}" "${IMAGE}:latest" && \
+          docker push "${IMAGE}:latest" && \
+          echo "Tagged and pushed: ${IMAGE}:latest (from ${{ steps.sha.outputs.short_sha }})"
+
+      - name: Prune images
+        run: docker image prune -a --force 2>&1 | tail -3 || true