Audit prop budgets and add a prop-gallery art check

- audit_glb decodes geometry: 400 tris / 600 verts budget, degenerate
  triangles, UV range, ground contact, one material; newspaper box parts moved
  to sit on y=0
- capture_prop_gallery.gd renders the six props on a studio backdrop; new
  prop_gallery catalogue entry + AI mockup (compare 10 good, judge match 0.90)
- headless test that instances share the imported atlas material
- README documents the gallery capture and budget; TODO props pipeline section
  moved to DONE

tools/screen_designs.py

@@ -495,6 +495,26 @@ SCREENS = [
             (0.02, 0.20, 0.36, 0.65, "reaction log"),
             (0.02, 0.94, 0.98, 0.99, "control hints"),
         ],
+    },    {
+        "name": "prop_gallery",
+        "kind": "scene",
+        "title": "Prop gallery",
+        "source": "tools/model_pipeline.py · docs screenshot set",
+        "ref": "10-prop-gallery.png",
+        "description": "Line-up of the six generated street-furniture props — a bollard, "
+                       "bench, trash bin, planter box, newspaper box and fire hydrant — on "
+                       "a plain studio backdrop, used as a close-range art check.",
+        "prompt": (
+            "Product line-up photograph of six low-poly 3D street-furniture props on a "
+            "plain light grey studio backdrop with a low display platform: a black steel "
+            "bollard, a wooden bench with black legs, a dark green trash bin, a white "
+            "planter box with a green hedge, a blue newspaper vending box and a red fire "
+            "hydrant. Even soft studio lighting, straight-on wide shot, muted realistic "
+            "colours, no people, no street context"),
+        "regions": [
+            (0.22, 0.14, 0.80, 0.47, "back row: planter, newspaper box, hydrant"),
+            (0.22, 0.38, 0.80, 0.68, "front row: bollard, bench, bin"),
+        ],
     },
 ]