Bake library AO and lift environment textures

Phase 4 of the v0.6.0 graphics plan:

- tools/bake_ao.py bakes 256² AO maps for every Blender character/gear/prop
  (Cycles, existing UVs) next to each GLB; Materials.apply_ao() wires the red
  channel into character slots, gear, and props. Compatibility has no SSAO.
- Regenerated brick/concrete/asphalt at 1024² with OpenRouter, derived tangent
  normal maps via tools/make_normal_maps.py, and wired them through
  SurfaceMaterials.textured() without changing UV scales.
- Evaluated Forward+: boots on desktop Vulkan, but the renderer is project-wide
  and Web must stay GL Compatibility; v0.6.0 keeps Compatibility (decision in
  MEMORY/plan). A desktop-only override is deferred.
- Recaptured screenshots; compare 11 good / 0 bad. Fixed marquee text alignment.
- Tests: baked AO maps exist for all 46 assets; prop/character AO material
  checks; headless 222/222, Python 69/69, all smokes pass.
- Version 0.6.0; ADR-0013 accepted; README/architecture/blender-assets/plan and
  TODO/DONE updated.

src/game/npc_avatar.gd

@@ -453,6 +453,8 @@ func _apply_outfit_materials(npc_type: int, outfit: Dictionary, cloth: Color,
 		"hair": outfit["hair"],
 		"accessory": Color(0.10, 0.11, 0.14),
 	}
+	var ao := Materials.load_ao(
+		BLENDER_NPC_DIR + character_model + "_ao.png")
 	for index in mesh.get_surface_count():
 		var source := mesh.surface_get_material(index)
 		if source == null:
@@ -462,8 +464,12 @@ func _apply_outfit_materials(npc_type: int, outfit: Dictionary, cloth: Color,
 		# (hivis, reflective, leather, steel, ...) keep their authored colour.
 		if not tints.has(slot):
 			continue
-		_skinned_mesh.set_surface_override_material(index,
-			Materials.npc_slot(source, tints[slot]))
+		var material := Materials.npc_slot(source, tints[slot])
+		if ao != null:
+			material.ao_enabled = true
+			material.ao_texture = ao
+			material.ao_texture_channel = BaseMaterial3D.TEXTURE_CHANNEL_RED
+		_skinned_mesh.set_surface_override_material(index, material)
 
 func _bind_bones() -> void:
 	_bone_indices.clear()
@@ -726,6 +732,9 @@ func _attach_gear(gear_name: String) -> bool:
 			node.free()
 			return false
 	_detail_nodes.append(node)
+	var ao := Materials.load_ao(BLENDER_GEAR_DIR + gear_name + "_ao.png")
+	for child in node.find_children("*", "MeshInstance3D", true, false):
+		Materials.apply_ao(child as MeshInstance3D, ao)
 	return true
 
 ## Character-specific library gear (firefighter helmet/SCBA, dress bag, vest