Add docker workflow

.gitea/workflows/docker.yaml

@@ -0,0 +1,34 @@
+name: Docker Build & Push
+
+on:
+  push:
+    branches: [ main ]
+
+jobs:
+  build-docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+      - name: Install nix
+        uses: cachix/install-nix-action@v31
+      - name: Setup cachix cache for devenv
+        uses: cachix/cachix-action@v16
+        with:
+          name: devenv
+      - name: Install devenv.sh
+        run: nix profile install nixpkgs#devenv
+
+      - name: Build the devenv shell and run any pre-commit hooks
+        run: devenv test
+
+      - name: Log in to Docker registry
+        shell: devenv shell bash -- -e {0}
+        run: |
+          docker login --username "${{ secrets.DOCKER_USERNAME }}" --password "${{ secrets.DOCKER_PASSWORD }}" "${{ secrets.DOCKER_REGISTRY }}"
+
+      - name: Build and push Docker image
+        shell: devenv shell bash -- -e {0}
+        run: |
+          docker build -t ${{ secrets.DOCKER_REGISTRY }}/sheetless/sheetless-frontend:${{ gitea.ref_name }} .
+          docker push ${{ secrets.DOCKER_REGISTRY }}/sheetless/sheetless-frontend:${{ gitea.ref_name }}