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

src/test/capture_prop_gallery.gd

@@ -0,0 +1,104 @@
+extends SceneTree
+## Dev helper: render every generated prop side by side on a plain backdrop and
+## save user://screenshots/10-prop-gallery.png. The image feeds
+## `tools/screen_designs.py compare` so a prop regression is visible.
+##
+## Usage: godot --path . --script res://src/test/capture_prop_gallery.gd
+
+const OUT_DIR := "user://screenshots"
+const MODEL_DIR := "res://assets/models/generated/"
+const PROPS := ["bollard", "bench", "trash_bin", "planter_box",
+	"newspaper_box", "fire_hydrant"]
+const SPACING := 1.9
+
+var frames := 0
+
+func _initialize() -> void:
+	root.size = Vector2i(1280, 720)
+	_build_stage()
+
+func _build_stage() -> void:
+	var stage := Node3D.new()
+	stage.name = "PropGallery"
+	root.add_child(stage)
+
+	var environment := Environment.new()
+	environment.background_mode = Environment.BG_COLOR
+	environment.background_color = Color(0.52, 0.54, 0.58)
+	environment.ambient_light_source = Environment.AMBIENT_SOURCE_COLOR
+	environment.ambient_light_color = Color(0.78, 0.80, 0.84)
+	environment.ambient_light_energy = 0.8
+	var world_env := WorldEnvironment.new()
+	world_env.environment = environment
+	stage.add_child(world_env)
+
+	# Floor and a plain backdrop wall: a studio line-up with no street context.
+	var floor_mesh := PlaneMesh.new()
+	floor_mesh.size = Vector2(14, 8)
+	var floor := MeshInstance3D.new()
+	floor.mesh = floor_mesh
+	floor.material_override = _flat(Color(0.50, 0.51, 0.54), 0.9)
+	stage.add_child(floor)
+
+	var backdrop_mesh := BoxMesh.new()
+	backdrop_mesh.size = Vector3(14, 6, 0.1)
+	var backdrop := MeshInstance3D.new()
+	backdrop.mesh = backdrop_mesh
+	backdrop.material_override = _flat(Color(0.55, 0.57, 0.61), 0.95)
+	backdrop.position = Vector3(0, 3.0, -3.4)
+	stage.add_child(backdrop)
+
+	# Raised back row so both rows read in a single shot.
+	var platform_mesh := BoxMesh.new()
+	platform_mesh.size = Vector3(6.8, 0.8, 1.9)
+	var platform := MeshInstance3D.new()
+	platform.mesh = platform_mesh
+	platform.material_override = _flat(Color(0.38, 0.39, 0.42), 0.85)
+	platform.position = Vector3(0, 0.4, -2.1)
+	stage.add_child(platform)
+
+	var light := DirectionalLight3D.new()
+	light.rotation_degrees = Vector3(-48, -35, 0)
+	light.light_energy = 0.85
+	light.shadow_enabled = true
+	stage.add_child(light)
+
+	var camera := Camera3D.new()
+	camera.position = Vector3(0, 2.1, 6.2)
+	camera.fov = 50.0
+	camera.look_at_from_position(camera.position, Vector3(0, 0.75, -1.0))
+	camera.current = true
+	stage.add_child(camera)
+
+	# 3 x 2 grid: three props on the front row, three on the back row.
+	var columns := [-1.95, 0.0, 1.95]
+	for index in PROPS.size():
+		var prop_name: String = PROPS[index]
+		var packed := ResourceLoader.load(MODEL_DIR + prop_name + ".glb") as PackedScene
+		if packed == null:
+			continue
+		var model := packed.instantiate() as Node3D
+		var col: int = index % 3
+		var row: int = index / 3
+		model.position = Vector3(columns[col], 0.8 if row == 1 else 0.0, -2.1 * row)
+		model.rotation_degrees.y = 14.0
+		stage.add_child(model)
+
+func _flat(color: Color, roughness: float) -> StandardMaterial3D:
+	var material := StandardMaterial3D.new()
+	material.albedo_color = color
+	material.roughness = roughness
+	return material
+
+func _process(_delta: float) -> bool:
+	frames += 1
+	if frames < 20:
+		return false
+	var dir := DirAccess.open("user://")
+	if dir == null or not dir.dir_exists("screenshots"):
+		dir.make_dir_recursive("screenshots")
+	var image := root.get_texture().get_image()
+	var err := image.save_png(OUT_DIR.path_join("10-prop-gallery.png"))
+	print("10-prop-gallery.png -> err=%d (%dx%d)" % [err, image.get_width(), image.get_height()])
+	quit(0)
+	return true

src/test/tests/test_generated_props.gd

@@ -68,6 +68,34 @@ func test_prop_scenes_share_one_atlas_material() -> bool:
 		instance.free()
 	return TestUtils.check(problems.is_empty(), "one atlas material per prop (%s)" % str(problems))
 
+func test_prop_instances_share_the_imported_material() -> bool:
+	## Instancing a prop must not duplicate its atlas material; every copy uses
+	## the same resource, so many props stay cheap to draw.
+	var problems: Array[String] = []
+	for prop in WorldBuilder.MODEL_PROPS:
+		var packed := ResourceLoader.load(MODEL_DIR + str(prop) + ".glb") as PackedScene
+		if packed == null:
+			problems.append("%s: no scene" % prop)
+			continue
+		var first := packed.instantiate()
+		var second := packed.instantiate()
+		var a := _first_material(first)
+		var b := _first_material(second)
+		if a == null or b == null:
+			problems.append("%s: missing material" % prop)
+		elif a.get_instance_id() != b.get_instance_id():
+			problems.append("%s: material is duplicated per instance" % prop)
+		first.free()
+		second.free()
+	return TestUtils.check(problems.is_empty(), "prop instances share materials (%s)" % str(problems))
+
+func _first_material(instance: Node) -> Material:
+	for node in instance.find_children("*", "MeshInstance3D", true, false):
+		var mesh: Mesh = (node as MeshInstance3D).mesh
+		if mesh != null and mesh.get_surface_count() > 0:
+			return mesh.surface_get_material(0)
+	return null
+
 func test_world_places_generated_props() -> bool:
 	var root := Node3D.new()
 	var builder := WorldBuilder.new(root)