fix: add cameleer user to root group for Docker socket access

The mounted /var/run/docker.sock is owned by root:root with rw-rw----
permissions. The cameleer user needs to be in the root group to
read/write the socket for building images and managing containers.

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

Dockerfile

@@ -24,6 +24,7 @@ RUN --mount=type=cache,target=/root/.m2/repository ./mvnw package -DskipTests -B
 FROM eclipse-temurin:21-jre-alpine
 WORKDIR /app
 RUN addgroup -S cameleer && adduser -S cameleer -G cameleer \
+ && addgroup cameleer root \
  && mkdir -p /data/jars && chown -R cameleer:cameleer /data
 COPY --from=build /build/target/*.jar app.jar
 USER cameleer