Log reason when inference logging is skipped

Prints which env var is missing instead of returning silently,
making it easier to diagnose missing HF_TOKEN or LOG_DATASET_REPO.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

logging_utils.py

@@ -25,6 +25,7 @@ def _readme_from_features(feats):
 def log_inference(pil_inputs, output_pil, prompt, seed, steps, guidance_scale,
                   input_width, input_height, duration_seconds, success, error_message=""):
     if not HF_TOKEN or not DATASET_REPO:
+        print(f"[log] skipped — HF_TOKEN={'set' if HF_TOKEN else 'missing'}, DATASET_REPO={'set' if DATASET_REPO else 'missing'}")
         return
     try:
         import tempfile, json as _json