feat(ar-024): enforce the invariant statically, and delete the fallback it caught

AR-024's register row gives its verification tier as "Static check -- no
bare cosine outside a tagged EXCEPTION". No such check existed, so the
invariant was enforced by reading, and reading had missed a live
violation.

scripts/ci/check_raw_cosine.py is that check, wired into the
traceability workflow as a blocking step. It is honest about its reach:
it catches direct cosine_similarity() uses not routed through a
calibration, and it cannot follow a cosine through a variable across
statements. That limit is documented in the script rather than left for
someone to discover after trusting a pass.

What it caught, and what this commit removes with it:

The identity matcher's no-calibration fallback thresholded raw cosine
distance (match_threshold) plus a ratio test (match_ratio,
match_ratio_ceil). Worse than the invariant breach: it fed
max(0, cosine) into TrackRegistry::observe, whose contract reads
"posterior is a calibrated probability, never a raw cosine (AR-024) ...
so the accumulation cannot be fed an uncalibrated number by a careless
caller". It could, and did. And it disagreed with the rest of the
pipeline about what "the fit failed" means -- same_person_probability
answers that with the untuned default sigmoid and a loud warning, so
association stayed in probability space while matching alone left it.
One run, two policies, no announcement.

Now one rule: cal_.probability() always, with a warning when the fit is
not real. A worse answer than a fitted calibration, a better one than a
number whose units nothing else shares.

TrackGallery::set_calibration is mandatory for the same reason. Its
default was max(0, cosine), which made expand_band_lo = 0.90 mean
"cosine > 0.9" in a test and "P(same person) > 0.9" in production.
FaceTrackerFunc already threw without one; the expansion store now
matches.

One exception is recorded, in the calibration's own dedup. It is not a
close call: at 1 - 1e-7 it asks whether two vectors are the same vector,
and it runs on the fit's input, so a calibrated comparison there would
have to be calibrated by the fit it is feeding.

Also drops seven dead keys from the optimizer's CFG_KEYS. Config keys
are read with a contains() check, so each one had been silently inert
since the field behind it was deleted -- a sweep varying one of them
measured nothing and reported an ordinary-looking F1.

TRACES: AR-024, AR-023 | SR-002

src/config.hpp

@@ -78,9 +78,15 @@ struct Config {
     // earlier 9-film scene-union-metric tuning (0.76) — that metric is now known to
     // have hidden out-of-cast false positives (see docs/optimizer-experiments.md).
     float       prob_threshold{0.754f};   // posterior P(match | sim, prior) threshold
-    float       match_threshold{0.45f};   // cosine distance hard ceiling fallback (no calibration)
-    float       match_ratio{0.80f};       // ratio test fallback: accept if best/second < ratio
-    float       match_ratio_ceil{0.65f};  // ratio test only fires below this absolute distance
+    // TRACES: AR-024 | SR-002
+    // match_threshold (0.45), match_ratio (0.80) and match_ratio_ceil (0.65) are
+    // RETIRED, joining track_max_embed_dist, cut_revive_sim, expand_novelty_sim
+    // and expand_track_spread_max. All were raw cosine distances, and they were
+    // the accept rule whenever the calibration fit failed — so the one situation
+    // in which the pipeline knew its probabilities were untrustworthy was the
+    // one in which it stopped using them. An unfitted sigmoid is now the
+    // fallback everywhere, which is at least the same wrong number in every
+    // stage. See identity_matcher_node.hpp.
 
     // ── Cut detection ────────────────────────────────────────────────────────
     float cut_threshold{0.70f};         // grayscale histogram correlation below this → hard cut