fix: skip frontend config tests when frontend/ dir absent (Docker build)

tests/unit/test_frontend_build_config.py

@@ -6,9 +6,17 @@ Prevents re-introducing JS obfuscation plugins that break vendor libraries
 import json
 from pathlib import Path
 
+import pytest
+
 FRONTEND_DIR = Path(__file__).resolve().parents[2] / "frontend"
 
+_skip_no_frontend = pytest.mark.skipif(
+    not FRONTEND_DIR.is_dir(),
+    reason="frontend/ directory not present (e.g. backend-only Docker build)",
+)
 
+
+@_skip_no_frontend
 class TestViteConfig:
     """Validate vite.config.ts doesn't contain dangerous build plugins."""