docs: four focused findings pages (best model, gallery scope, expansion, deep dive)

Splits the rep4 write-up's key findings into their own linkable pages:
- best-model.md: calibration curves first (discriminative power, independent
  of any threshold), then F1 on the benchmark — LVFace-B Glint360K wins both.
- gallery-scope.md: whole vs. cast-restricted gallery, isolated from model and
  expansion choice — restriction wins on every axis, but isn't a shipped
  runtime feature yet.
- pose-expansion.md: the training-set expand_gallery effect, and the held-out
  replication attempt that found it doesn't reproduce (5 films, 2 models,
  after catching and fixing a replay-timeout truncation bug and a bbox
  first-match-instead-of-best-match bug in the comparison harness itself). An
  honest null result, with the methodology errors documented since they're
  exactly the kind that manufacture a false "it works!" finding.
- lvface-deep-dive.md: the winning model's held-out generalization gap, its
  two failure modes (frozen-bbox ghost tracks), and a verified case (cross-
  checked against Jellyfin's independent cast metadata) where LVFace
  correctly identified an actor that X-Ray's ground truth failed to credit.

Adds a "report-highlights" artifact-registry package (scripts/artifacts/
push_artifacts.sh, pull_artifacts.sh) for hand-picked illustrative frames that
aren't reproducible via the automated best/worst montage selection, and wires
pulling it into scripts/docs/build_site.sh.

scripts/docs/build_site.sh

@@ -26,6 +26,11 @@ cp -v "${FRAMES_ROOT}/many_saints/fpi/fpi_t03543.jpg" \
 cp -v "${FRAMES_ROOT}/downton_abbey/fpi/fpi_t07242.jpg" \
       "${ASSETS_DIR}/downton_abbey_ghost_fpi.jpg"
 
+if [ ! -f "${ASSETS_DIR}/germar_beats_xray.jpg" ]; then
+    echo "==> pulling report-highlights/germar_beats_xray.jpg..."
+    scripts/artifacts/pull_artifacts.sh report-highlights germar_beats_xray.jpg
+fi
+
 if [ ! -d experiments/galleries ] || [ -z "$(ls -A experiments/galleries 2>/dev/null)" ]; then
     echo "==> pulling galleries (not found locally)..."
     scripts/artifacts/pull_artifacts.sh galleries