fix: add back _resolve_image_tag for test compatibility [skip-version]

Author: localpibox

scripts/lpb.py

@@ -166,6 +166,11 @@ def _resolve_version_image(version: str, mode: str) -> str:
     return f"ghcr.io/localpibox/devstack:{version}-{mode}"
 
 
+def _resolve_image_tag() -> str:
+    """Return the image tag suffix from env var (legacy compatibility)."""
+    return os.environ.get("LPB_IMAGE_TAG", "")
+
+
 def resolve_cli_image(tag: str) -> str:
     """Resolve the final CLI image name from stack config + tag override.