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/test_model_pipeline.py

@@ -195,6 +195,43 @@ class AuditTests(unittest.TestCase):
         self.assertFalse(result["ok"])
         self.assertTrue(result["issues"])
 
+    def test_audit_enforces_the_triangle_budget(self):
+        old = model_pipeline.MAX_TRIANGLES
+        model_pipeline.MAX_TRIANGLES = 10
+        try:
+            path = self.root / "bench.glb"
+            path.write_bytes(model_pipeline.build_glb(prop("bench")))
+            result = model_pipeline.audit_glb(path)
+        finally:
+            model_pipeline.MAX_TRIANGLES = old
+        self.assertFalse(result["ok"])
+        self.assertTrue(any("triangle budget" in issue for issue in result["issues"]),
+                        result["issues"])
+
+    def test_degenerate_triangle_helper(self):
+        self.assertEqual(
+            model_pipeline._triangle_area2((0, 0, 0), (1, 0, 0), (2, 0, 0)), 0.0)
+        self.assertGreater(
+            model_pipeline._triangle_area2((0, 0, 0), (1, 0, 0), (0, 1, 0)), 0.0)
+
+    def test_audit_reads_positions_and_uvs_from_the_binary(self):
+        parsed = parse_glb(model_pipeline.build_glb(prop("bollard")))
+        gltf, binary = parsed["gltf"], parsed["binary"]
+        primitive = gltf["meshes"][0]["primitives"][0]
+        positions = model_pipeline._read_float_accessor(
+            gltf, binary, primitive["attributes"]["POSITION"])
+        uvs = model_pipeline._read_float_accessor(
+            gltf, binary, primitive["attributes"]["TEXCOORD_0"])
+        indices = model_pipeline._read_index_accessor(
+            gltf, binary, primitive["indices"])
+        self.assertEqual(len(positions), gltf["accessors"][
+            primitive["attributes"]["POSITION"]]["count"])
+        self.assertEqual(len(uvs), len(positions))
+        self.assertEqual(len(indices) % 3, 0)
+        self.assertLess(min(p[1] for p in positions), 0.01)
+        for u, v in uvs:
+            self.assertTrue(0.0 <= u <= 1.0 and 0.0 <= v <= 1.0)
+
     def test_build_writes_into_the_models_directory(self):
         old = model_pipeline.MODELS_DIR
         model_pipeline.MODELS_DIR = self.root