refactor(config): give the tuned constants a real provenance, and make them reachable

Two problems, both of which made a number look more settled than it is.

The provenance was a dead link. config.hpp cited
docs/rep4-optimizer-results.md for prob_threshold, extinction_sec,
anneal_sec and the expansion default. That file was renamed to
model-bakeoff.md and then rewritten; the comments were never repointed,
so the most consequential constant in the pipeline appeared to have no
source at all.

Following it up produced something worse than a broken link.
prob_threshold=0.754 comes from the ORIGINAL rep4 document (still
readable at `git show d340da7:docs/rep4-optimizer-results.md`). The
rewrite that replaced it reports finding "a real scoring bug in
optimize.py: a candidate whose hardest film's replay timed out was
averaged over survivors instead of penalized, silently rewarding partial
coverage. Affected 3 of 16 training combos". So 0.754 was fitted under
scoring that was later found wrong, the corrected sweep converged
elsewhere, and no corrected prob_threshold is recorded anywhere. The
comment now says that, along with the surviving document's own verdict
that the optimum "generalizes unevenly -- strong on 3 of 5 held-out
films, badly broken on 2".

Four constants were unreachable. ownership_logodds lived on
TrackRegistry::Config, and max_views/admit_below/rho_max on
EvidenceDiscounter::Config, which main built with the one-argument
constructor -- so nothing short of a recompile could move any of them.
rho_max's own comment defers to "the sweep (VR-007)" for where it
belongs, and that sweep could not reach it.

They now live in Config with CLI flags and are exposed to the replay
harness. ownership_logodds is worth singling out: below it a track makes
no presence claim at all, so it decides whether an actor is reported
rather than how confidently -- arguably the most consequential constant
after prob_threshold, and until now unswept and unsettable.

No behaviour change: every default is the value that was compiled in.

TRACES: AR-025, AR-017 | SR-002

src/kpn_bindings.cpp

@@ -173,6 +173,11 @@ static Config config_from_dict(nb::dict d) {
     getf("track_min_iou",         cfg.track_min_iou);
     getf("track_assoc_min_prob",  cfg.track_assoc_min_prob);
     getd("track_extinction_sec",  cfg.track_extinction_sec);
+    // AR-025: swept knobs, previously unreachable from any config.
+    getf("ownership_logodds",     cfg.ownership_logodds);
+    getf("evidence_rho_max",      cfg.evidence_rho_max);
+    getf("evidence_admit_below",  cfg.evidence_admit_below);
+    geti("evidence_max_views",    cfg.evidence_max_views);
     // gallery expansion (usually off for sweeps; expose so it can be toggled)
     if (d.contains("expand_gallery")) cfg.expand_gallery = nb::cast<bool>(d["expand_gallery"]);
     /// TRACES: GR-004 | SR-001