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/make_normal_maps.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Derive tangent-space normal maps from albedo textures (Pillow only).
+
+    python3 tools/make_normal_maps.py assets/textures/ai/game_ready/brick_facade.png ...
+
+Writes <stem>_normal.png next to each input. The height signal is the
+luminance, so mortar/aggregate recesses catch the light; edges wrap for tiling.
+"""
+
+import sys
+from pathlib import Path
+
+from PIL import Image
+
+STRENGTH = 2.0
+
+
+def normal_map(source: Path) -> Path:
+    image = Image.open(source).convert("L")
+    width, height = image.size
+    pixels = list(image.getdata())
+    out = bytearray(width * height * 3)
+
+    def lum(x: int, y: int) -> float:
+        return pixels[(y % height) * width + (x % width)]
+
+    for y in range(height):
+        row = y * width
+        for x in range(width):
+            dx = (lum(x + 1, y) - lum(x - 1, y)) / 255.0
+            dy = (lum(x, y + 1) - lum(x, y - 1)) / 255.0
+            nx = -dx * STRENGTH
+            ny = -dy * STRENGTH
+            nz = 1.0
+            length = (nx * nx + ny * ny + nz * nz) ** 0.5
+            offset = (row + x) * 3
+            out[offset] = int((nx / length * 0.5 + 0.5) * 255)
+            out[offset + 1] = int((ny / length * 0.5 + 0.5) * 255)
+            out[offset + 2] = int((nz / length * 0.5 + 0.5) * 255)
+    normal = Image.frombytes("RGB", (width, height), bytes(out))
+    target = source.with_name(source.stem + "_normal.png")
+    normal.save(target)
+    print(f"wrote {target}")
+    return target
+
+
+def main(argv=None) -> int:
+    paths = [Path(p) for p in (argv if argv is not None else sys.argv[1:])]
+    if not paths:
+        print(__doc__, file=sys.stderr)
+        return 2
+    for path in paths:
+        normal_map(path)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())