Refactor backend and add registry build workflow

.gitea/workflows/docker.yml

@@ -0,0 +1,49 @@
+name: Build and publish Docker image
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  packages: write
+
+jobs:
+  build-and-publish:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out source
+        uses: actions/checkout@v4
+
+      - name: Log in to Gitea Container Registry
+        env:
+          REGISTRY_USERNAME: ${{ gitea.actor }}
+          REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          printf '%s' "$REGISTRY_TOKEN" |
+            docker login git.anchorhost.eu --username "$REGISTRY_USERNAME" --password-stdin
+
+      - name: Build and tag image
+        env:
+          COMMIT_SHA: ${{ gitea.sha }}
+          DOCKER_IMAGE: git.anchorhost.eu/anchorhost.eu/anchorhost-backend
+        run: |
+          docker build \
+            --label "org.opencontainers.image.revision=$COMMIT_SHA" \
+            --tag "$DOCKER_IMAGE:backend" \
+            --tag "$DOCKER_IMAGE:main-${COMMIT_SHA:0:12}" \
+            .
+
+      - name: Push image
+        env:
+          COMMIT_SHA: ${{ gitea.sha }}
+          DOCKER_IMAGE: git.anchorhost.eu/anchorhost.eu/anchorhost-backend
+        run: |
+          docker push "$DOCKER_IMAGE:backend"
+          docker push "$DOCKER_IMAGE:main-${COMMIT_SHA:0:12}"
+
+      - name: Log out from Gitea Container Registry
+        if: always()
+        run: docker logout