Add registry authentication using Gitea automatic secrets

Use GITEA_ACTOR and GITEA_TOKEN for Docker registry login. These secrets
are automatically provided by Gitea Actions and require no manual
configuration.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -28,6 +28,13 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
+      - name: Login to Registry
+        # Gitea automatically provides these secrets:
+        # - GITEA_ACTOR - The username of the user who triggered the workflow
+        # - GITEA_TOKEN - An automatically generated token with appropriate permissions
+        run: |
+          echo "${{ secrets.GITEA_TOKEN }}" | docker login registry.budakova.org -u "${{ secrets.GITEA_ACTOR }}" --password-stdin
+
       - name: Build and push Docker image
         uses: docker/build-push-action@v5
         with: