feat(tex): ComfyUI tool, procedural character textures, hair cap behind a flag

Tools/comfyui_generate.py drives the local ComfyUI instance for generated textures
and writes a sidecar with model, prompt, seed and workflow, so a generated asset can
be regenerated or rejected instead of being an unexplained PNG. Models list and
generation both verified against 127.0.0.1:8188.

Stable Diffusion is not usable for flat skin swatches, and that is worth recording:
three attempts produced an anatomical close-up twice and a leather-scale surface once.
Skin detail is generated procedurally instead - tileable octave noise for pores, plus
a strand sheet for hair - in Tools/generate_character_textures.py, with sidecars.

Hair geometry exists (cap conforming to the head, weighted to the head bone, second
material slot in Blender) but Unreal's import collapses the second material slot, so
the cap renders with the skin material and reads as a bald skull. It is behind
--hair and off; the next step is a separate skeletal mesh attached as a second
component.

TODO.md

@@ -15,7 +15,11 @@ Actionable task list for this project. This file is the single, central place fo
 
 - [x] Restore the stride capture after the pose rewrite. The walk cycle started on a **sine**, zero at both the start and the middle of the cycle, so the deterministic capture kept landing on the two passing frames where the legs are together. Starting the cycle at maximum stride (cosine) fixed it with no other change; `demo-third-person-walk` is back as shot 8 and shows a genuine stride.
 
-- [ ] Tune skin shading and hair materials on the player character.
+- [A] Tune skin shading and hair materials on the player character. **Tooling in place 2026-11-09, hair blocked on an engine-side limit:**
+  - `Tools/comfyui_generate.py` drives the local ComfyUI instance (`127.0.0.1:8188`) for textures, writing a JSON sidecar with the model, prompt, seed and full workflow so anything generated can be regenerated or rejected. Installed models include `juggernautXL_ragnarok.safetensors` and `sd-v1-5-inpainting.ckpt`.
+  - **Stable Diffusion is not usable for flat skin swatches.** Three attempts on two models produced an anatomical close-up twice and a leather-scale surface once; SDXL has no reliable notion of "texture without anatomy". Skin detail is therefore generated procedurally instead (`Tools/generate_character_textures.py`: tileable octave noise for pores plus a strand-sheet texture for hair).
+  - **Hair geometry is built but not shipped.** `add_hair_cap()` creates a cap conforming to the head and weights it to the `head` bone (Blender shows two material slots, hair faces on index 1), but Unreal's import **collapses the second material slot**, so the cap renders with the skin material and reads as a bald skull. It is behind `--hair`, off. Next step: export the hair as its own skeletal mesh and attach it as a second component, or bake the hair colour into vertex colours.
+
 - [ ] Tag `v0.2.2` and write `CHANGELOG.md` entry; then remove this section.
 
 ## 0.2.3 — Camera clipping fixes (patch)