fix(refract): null skipped axis score in JSON + 'skip' in compare table

Audit follow-up to the earlier skip-axis fix (728cd84). The stub axis
result dataclasses still carry score=100, so without these changes:

- json_report still wrote 'axes.gtm.score: 100.0' for a skipped axis,
  visible to anyone parsing the JSON or running 'refract compare'
- 'refract compare' showed 100.0 in the Traj/KLD column for skipped
  reports, which made cross-report comparison falsely flatter the
  skipped run

Now: when CompositeScore.gtm_score is None we write axes.gtm.score = null
in the JSON. 'refract compare' reads 'skipped' or score=None and prints
'skip' in that column instead of the stub 100.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-Authored-By: tturney1@gmail.com <tturney1@gmail.com>

Author: TheTom

refract/cli.py

@@ -808,7 +808,10 @@ def _run_compare(args) -> int:
         a = r["axes"]
         def fmt(d, k):
             try:
-                return f"{a[k]['score']:.2f}"
+                ax = a[k]
+                if ax.get("skipped") or ax.get("score") is None:
+                    return "skip"
+                return f"{ax['score']:.2f}"
             except Exception:
                 return "—"
         comp_val = r["composite"]

refract/report.py

@@ -338,6 +338,14 @@ def json_report(
     composite_band = composite_dict.pop("band")
     def _band_or_skipped(s):
         return band(s) if s is not None else "skipped"
+    # When an axis was skipped, the underlying result dataclass still has a
+    # stub score=100. Null out the JSON 'score' field so downstream readers
+    # (compare, leaderboards, paper tables) don't pick up the stub as real.
+    if composite.gtm_score is None:
+        gtm_dict["score"] = None
+    kld_dict = asdict(kld)
+    if composite.kld_score is None:
+        kld_dict["score"] = None
     axes_block: dict = {
         "gtm": {
             **gtm_dict,
@@ -346,7 +354,7 @@ def _band_or_skipped(s):
             "description": _AXIS_PROSE["gtm"],
         },
         "kld": {
-            **asdict(kld),
+            **kld_dict,
             "band": _band_or_skipped(composite.kld_score),
             "skipped": composite.kld_score is None,
             "description": _AXIS_PROSE["kld"],