refactor(bench): SuperHero replaces Road to Bali as the reference film

Bali was chosen because the TRECVID DVU set ships character mugshots, but
its reference crops are unusable at scale: median detected face 27 px
against a 69 px maximum, so every reference was upscaled 4x or more past
what the embedder was trained for (AR-011). A 66 px floor left 2 of 69
references; no threshold exists that both keeps the faces in distribution
and leaves enough of them to calibrate.

SuperHero is 69 px median and 241 px max. Its gallery builds at a 66 px
floor with 14 references over 5 characters, and calibrates on its own
(a=15.2867 b=-4.98633, 100% train accuracy) instead of borrowing constants.

Measured on the fused 17-minute film, one stream rather than per-scene
clips so presence windows cross real scene boundaries as SR-002 intends:
precision 1.00, recall 0.65, F1 0.79 — 13 true positives, 0 false
positives, 7 misses. Every out-of-gallery character was declined rather
than forced onto a nearest match. The misses are the short scenes (14 s,
38 s, 27 s), consistent with per-track accumulation needing sightings.

- build_gallery gains --min-face-px, filtering the *detected face* rather
  than the crop. The DVU images are scene crops, not mugshots, so crop
  dimensions say nothing about face scale. A poisoned reference is
  permanent in a way a bad frame is not: it corrupts every future match
  against that identity.
- scripts/fetch_dvu.sh fetches mugshots, scene graphs and segmentation for
  any DVU film. NIST names the same film three different ways, so KG_DIR
  and KG_FILE are overridable rather than derived. This exists as a script
  because the first copy of this data was assembled ad hoc in /tmp and was
  lost with it, taking the working gallery along.
- Replay fixtures move to the artifact registry: push/pull_artifacts.sh
  gain a replay-fixtures target, and tests/fixtures/dumps/.gitignore keeps
  them out of git. superhero.h5 is ~9 MB and regenerating it needs the
  film, the models and a GPU — none of which CI has. The gallery ships
  with the dumps, since a dump only replays against the gallery it was
  produced with.
- AR-012 and AR-013 coverage is ported onto the new fixture rather than
  dropped with the Bali cases: 12369 assertions, up from 7991, since the
  film is an order of magnitude larger than the clips.

Suite: 15679 assertions, 101 test cases.

TRACES: AR-011, AR-012, AR-013 | VR-001, VR-005 | SR-002

scripts/artifacts/pull_artifacts.sh

@@ -10,6 +10,7 @@
 #   scripts/artifacts/pull_artifacts.sh galleries [version]
 #   scripts/artifacts/pull_artifacts.sh montage-frames <film-slug> [version]
 #   scripts/artifacts/pull_artifacts.sh experiment-data [version]
+#   scripts/artifacts/pull_artifacts.sh replay-fixtures [version]
 #   scripts/artifacts/pull_artifacts.sh report-highlights <name> [version]
 #   scripts/artifacts/pull_artifacts.sh xsource [version]
 # version defaults to "latest" (newest uploaded version, by created_at).
@@ -42,6 +43,22 @@ print(matches[-1]['version'])
 "
 }
 
+pull_replay_fixtures() {
+    local version="$1"
+    local dest="${REPO_ROOT}/tests/fixtures/dumps"
+    mkdir -p "$dest"
+    echo "=== replay-fixtures (version ${version}) ==="
+    local tmp; tmp="$(mktemp -d)"
+    if curl -sf "${DL_BASE}/generic/replay-fixtures/${version}/replay-fixtures.zip" \
+            -o "${tmp}/f.zip"; then
+        unzip -qo "${tmp}/f.zip" -d "$dest"
+        echo "  restored: $(ls "$dest" | wc -l) files into tests/fixtures/dumps/"
+    else
+        echo "    [warn] replay-fixtures.zip not found at version ${version}" >&2
+    fi
+    rm -rf "$tmp"
+}
+
 pull_galleries() {
     local version="$1"
     local dest="${REPO_ROOT}/experiments/galleries"
@@ -181,8 +198,13 @@ case "$TARGET" in
         [ "$VERSION" = "latest" ] && VERSION="$(resolve_latest_version xsource)"
         pull_xsource "$VERSION"
         ;;
+    replay-fixtures)
+        VERSION="${2:-latest}"
+        [ "$VERSION" = "latest" ] && VERSION="$(resolve_latest_version replay-fixtures)"
+        pull_replay_fixtures "$VERSION"
+        ;;
     *)
-        echo "unknown target: $TARGET (expected galleries, montage-frames, experiment-data, report-highlights, or xsource)" >&2
+        echo "unknown target: $TARGET (expected galleries, montage-frames, experiment-data, report-highlights, xsource, or replay-fixtures)" >&2
         exit 1
         ;;
 esac