Fix group attribute syntax: use correct [group('name')] format

- Change all [group: 'name'] to [group('name')] per Just documentation
- Ensures compatibility with Just 1.21.0 and resolves 'Unknown attribute group' error
- Affects all just-commons files: container, volumes, postgres, mysql, images, registry, core

core.just

@@ -40,7 +40,7 @@ _detect_compose:
     fi
 
 # Environment detection and validation
-[group: 'environment']
+[group('environment')]
 env-check:
     #!/usr/bin/env bash
     set -euo pipefail