ci: build and push custom Logto image in CI pipeline

- Add "Build and push Logto image" step to docker job
- Remove build: directive from logto service in docker-compose
- docker-compose now only pulls pre-built images, no local builds

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -59,9 +59,6 @@ services:
 
   logto:
     image: ${LOGTO_IMAGE:-gitea.siegeln.net/cameleer/cameleer-logto}:${VERSION:-latest}
-    build:
-      context: .
-      dockerfile: docker/logto.Dockerfile
     restart: unless-stopped
     depends_on:
       postgres: