feat(qa): reference-vs-render iteration loop; screenshots are demo-only

Tools/visual_loop.py:
- --verify gates every capture against its expectation in Tools/visual_targets.json
  (missing, blank, tone-less or wrong-size shots fail), so 'each screenshot shows
  what was expected' is checked rather than assumed.
- --compare measures luminance, RMS contrast, edge density, palette distance and a
  3x3 luma grid against the reference photograph, with a 0-1 similarity score.
- --iteration N writes Art/reference/iterations/N/{metrics.json,feedback.md}; the
  feedback names the skill to consult (blender-modeler, archviz, materials, lookdev,
  camera-cinematography), so the next modelling pass starts from a measurement.
- Iterations are gitignored until the owner confirms a shot; only confirmed shots
  are promoted into Screenshots/.

Screenshots/ holds demo-map captures only now: render_screenshots.sh renders just
DemoMap, collects the shots and runs the verification gate (--verify); the review
staging map is no longer rendered for review and its PNGs are removed. The README
is rewritten around the four demo shots with per-shot expected content and a
verified column, and no longer claims the review staging set.

Tests: 67 pass (13 new) covering metrics on synthetic images, comparison scoring,
the feedback rules and the target spec (including that every target is a demo shot
and that iterations are gitignored).

Tools/render_screenshots.sh

@@ -1,56 +1,54 @@
 #!/usr/bin/env bash
-# Render in-game screenshots for visual review into <repo>/Screenshots/ (gitignored).
+# Render the demo-map screenshots used for visual review into <repo>/Screenshots/demo/.
 #
-# Usage: Tools/render_screenshots.sh
-# Rebuilds /Game/Test/ReviewMap and /Game/Hollywood/DemoMap (shot lists), runs
-# the game on each map (the GigLineShotActor walks the cameras, captures, quits),
-# and copies the PNGs into Screenshots/. PNGs are never committed.
+# Usage: Tools/render_screenshots.sh [--verify]
+#
+# Only the **demo map** is captured: the review staging map exists to hold the
+# hero/camera list, not to produce review screenshots. Everything here is what a
+# player actually sees when the demo runs.
+#
+#   --verify   run Tools/visual_loop.py --verify afterwards and fail if a shot
+#              does not show the content its expectation describes
+#
+# The PNGs are committed (see Screenshots/README.md): a reviewer must see exactly
+# what the build rendered.
 set -euo pipefail
 
 REPO="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 ENGINE="${UE_ENGINE_DIR:-/run/media/system/DATA/Engines/UE_5.8.4}"
 PROJ="$REPO/Game/GigLine/GigLine.uproject"
+VERIFY="no"
+[ "${1:-}" = "--verify" ] && VERIFY="yes"
 
-echo "== 1/4 build review + demo shot maps =="
+echo "== 1/3 stage the demo shot cameras =="
 cd "$ENGINE"
 ./Engine/Binaries/Linux/UnrealEditor-Cmd "$PROJ" \
   -run=pythonscript -script="$REPO/Tools/ue_build_review_map.py" \
   -nullrhi -unattended -nopause -stdout
-cat /tmp/ue-review-map-result.txt | tail -3
+tail -3 /tmp/ue-review-map-result.txt 2>/dev/null || true
 
-run_capture() {
-  local map="$1" label="$2"
-  echo "== capture: $label =="
-  ./Engine/Binaries/Linux/UnrealEditor-Cmd "$PROJ" "$map" \
-    -game -windowed -ResX=1920 -ResY=1080 -nopause -nosplash -stdout
-}
+echo "== 2/3 capture the demo map =="
+./Engine/Binaries/Linux/UnrealEditor-Cmd "$PROJ" /Game/Hollywood/DemoMap \
+  -game -windowed -ResX=1920 -ResY=1080 -nopause -nosplash -stdout
 
-echo "== 2/4 run game on review map (hero/scene shots) =="
-run_capture "/Game/Test/ReviewMap" "review"
-
-echo "== 3/4 run game on demo map (walkable-demo shots) =="
-run_capture "/Game/Hollywood/DemoMap" "demo"
-
-echo "== 4/4 collect screenshots =="
+echo "== 3/3 collect the demo screenshots =="
 mkdir -p "$REPO/Screenshots/demo"
-rm -f "$REPO"/Screenshots/review-*.png "$REPO"/Screenshots/demo/review-*.png
+rm -f "$REPO"/Screenshots/demo/review-*.png
 found=0
 for src in \
   "$REPO/Game/GigLine/Saved/Screenshots"/*/review-*.png \
   "$REPO/Game/GigLine/Saved/Screenshots"/*/*/review-*.png \
   "$HOME/.config/Epic/GigLine/Saved/Screenshots"/*/review-*.png; do
   [ -e "$src" ] || continue
-  name=$(basename "$src")
-  if [[ "$name" == review-?("")-demo-* || "$name" == review-*-demo-* || "$name" == review-0?-demo-* ]] \
-     || [[ "$name" == *demo-* ]]; then
-    cp -f "$src" "$REPO/Screenshots/demo/$name"
-  else
-    cp -f "$src" "$REPO/Screenshots/$name"
-  fi
-  found=1
+  case "$(basename "$src")" in
+    *demo-*) cp -f "$src" "$REPO/Screenshots/demo/"; found=1 ;;
+  esac
 done
-[ "$found" = "1" ] || { echo "ERROR: no review-*.png found"; exit 1; }
-echo "--- Screenshots/ ---"
-ls -1 "$REPO/Screenshots"
-echo "--- Screenshots/demo/ ---"
-ls -1 "$REPO/Screenshots/demo"
+[ "$found" = "1" ] || { echo "ERROR: no demo screenshots found"; exit 1; }
+ls -1 "$REPO/Screenshots/demo"
+
+if [ "$VERIFY" = "yes" ]; then
+  echo "== verify: does each shot show what it should? =="
+  cd "$REPO"
+  python3 Tools/visual_loop.py --verify
+fi