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.

tools/test_blender_assets.py

@@ -54,6 +54,15 @@ class BuiltAssetTests(unittest.TestCase):
             if entry["category"] == "npc_gear":
                 self.assertIn(entry["attach"], ba.GEAR_ATTACH, name)
 
+    def test_baked_ao_maps_exist_for_every_asset(self):
+        from PIL import Image
+        for name, entry in json.loads(
+                ba.MANIFEST.read_text(encoding="utf-8"))["assets"].items():
+            path = ba.OUT_DIR / entry["category"] / f"{name}_ao.png"
+            self.assertTrue(path.is_file(), path)
+            with Image.open(path) as image:
+                self.assertEqual(image.size, (256, 256), path)
+
     def test_sources_are_hidden_from_godot(self):
         self.assertTrue((ba.SRC_DIR / ".gdignore").is_file())