Reorganize docs into category folders and drop the retired head-review page

Group the top-level docs into docs/project, docs/design, docs/assets and
docs/process, each with its own README index. Delete the superseded
docs/screens/head-review page and sheets. Rewrite every markdown link,
absolute docs path and tool/test reference to the new locations, fix the
pre-existing broken anchors and remove the dead Joke Shop photo-board link.
check_docs OK, Python tooling 167/167.

docs/assets/makehuman-head-review.md

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+# MakeHuman head prototype
+
+Status: **retained fallback; superseded as the active NPC head by the Quaternius
+base (ADR-0017).** The owner accepted the basic human head on 2026-11-04. The automated vision gate
+still records REJECT on the eye/lid region as deferred polish. The asset is a
+standalone head/neck extracted from the CC0 MakeHuman base. The assembled path
+adds hair, a hidden scalp trim and the procedural body. The 12 shipped GLBs have
+not been rebuilt with it, and the Quaternius migration replaces it as the active
+base. The development source files were removed from `tmp/` on 2026-11-05.
+
+## Asset
+
+- GLB: [`assets/models/blender_src/makehuman_head.glb`](../../assets/models/blender_src/makehuman_head.glb)
+- Review sheet: [`blender_previews/sheet_makehuman_head.jpg`](../blender_previews/sheet_makehuman_head.jpg)
+- Source workflow (development-only, files removed after the Quaternius pivot;
+  retained here as the historical method) — extracts the MakeHuman head, cuts it at the neck, keeps the head/eye/mouth
+  components, cuts an almond aperture through a skin eyelid mask, adds recessed
+  eyeballs with flat iris/pupil discs, anchors brows to the face surface, renders
+  front/three-quarter/profile and exports the standalone GLB.
+- Measurements (final standalone build, `inspect`): **12,641 triangles / 7,690
+  split vertices**; bounds approximately `x ±0.094 m`, `y -0.180…0.042 m`,
+  `z 1.530…1.803 m` in project Z-up space.
+- Assembled `npc_casual --head mh`: **14,753 triangles / 12,823 seam-split
+  vertices / 14 bones / 9 materials**, `inspect` clean. All 12 variants count
+  14,693–15,987 triangles with the same head.
+- Materials used: `skin`, `eye_white`, `iris`, `pupil`, `hair`. No textures are
+  baked into this prototype.
+
+![MakeHuman head review sheet](../blender_previews/sheet_makehuman_head.jpg)
+
+## What was done
+
+1. Imported the CC0 MakeHuman base OBJ and cleared the importer axis rotation.
+2. Applied the project scale/axis transform: 1.82 m body, Z-up, metres,
+   front −Y.
+3. Cut the head at the neck (`z ≈ 1.53`) rather than keeping the cut shoulders;
+   capped the neck opening.
+4. Built an eyelid mask by subtracting an almond aperture from a skin sphere
+   centred on each eye (`solver = "EXACT"`), then recessed the globes so the
+   cornea sits behind the lid plane.
+5. Added flat iris/pupil discs on the globe axis; disabled backface culling so
+   the discs stay visible at three-quarter angles.
+6. Anchored brow strips to the skin with object-space ray casts and added a
+   shallow supraorbital ridge so they do not float, then reduced the crown
+   height to improve the profile silhouette.
+7. Fixed a material-remap bug introduced by joining the extra eye objects: the
+   joined head faces were pointing at the `eye_white` slot, making the whole
+   head render as white clay. The largest connected component is now forced
+   back onto `skin` after the join.
+8. Rendered front/three-quarter/profile views in a neutral review studio and
+   exported the standalone GLB.
+
+## Provenance
+
+- Base mesh: MakeHuman / MPFB base, CC0, from the local research set
+  (development source files removed after the 2026-11-05 Quaternius pivot); see
+  [`CREDITS.md`](../../CREDITS.md).
+- The head is a **derived prototype**, not a shipped NPC. It does not enter
+  `assets/models/blender/npc/`, `npc_base`, the runtime `NpcAvatar` path, CI, or
+  a release package. It is retained as a fallback, not the active NPC base.
+- Source photographs/proportions are not used as textures here; this is a
+  geometry-only head built from the researched model data.
+
+## Review criteria
+
+Accept only if:
+
+- the head reads as human at front/three-quarter/profile and the neck is a
+  clean head/bust silhouette, not a shoulder cut;
+- eyes, brow, nose, mouth and ears are readable without spikes, holes or
+  floating shells;
+- the asset is inside the character budget and has no script/contract violation;
+- the prototype remains clearly local and un-integrated until the part pipeline
+  is approved.
+
+## Judge result
+
+**Owner verdict: ACCEPT (basic human head, 2026-11-04).**
+**Automated vision gate: REJECT** (vision judge `z-ai/glm-5.3-flash`, final
+standalone build render set above). The eye/lid findings below remain deferred
+polish; they are no longer a rollout blocker because the owner accepted the head.
+
+Blocking findings:
+
+- **P0 — globe depth is inconsistent across views.** The front/three-quarter
+  reads still show a bead-like iris with a pale sclera halo, while the profile
+  reduces the eye to a brown sliver. The judge reads this as a faked recess
+  rather than a socketed globe under a lid.
+- **P0 — no convincing lid overlap.** The iris remains nearly circular in front
+  and the upper lid does not visibly clip the globe; the skin lid mask reads as
+  a crater around a bead.
+- **P0 — iris orientation reads decal-locked** at three-quarter, so the gaze
+  appears to drift off the head axis.
+- **P0 — the aperture/lid mask is too circular** and lacks medial/lateral
+  canthi, so the eye still reads as a doll eye at portrait distance.
+
+Should-fix findings:
+
+- the brow tubes are better anchored but the medial ends still detach in
+  three-quarter/profile;
+- nose lacks a defined tip/wing and nostrils;
+- mouth is a faint geometric seam with no lip volume;
+- crown/back-of-skull is still faceted and egg-like in profile;
+- the catchlight is baked geometry and is not consistent between eyes.
+
+What passed: the skin/eye material remap is correct, the eye openings are
+closed, the standalone GLB reports **12,641 triangles / 7,690 split vertices**,
+and an assembled `npc_casual` with this head passes `inspect` at **14,753 /
+16,000 triangles, 12,823 seam-split vertices, 14 bones, no issues**.
+
+Known limits: bald mannequin-like presentation, stylized geometry-only
+iris/pupil, no rig, no UV texture pass, and the neck cap is a review cut rather
+than a body-welded seam.
+
+## Assembled prototype (2026-11-04)
+
+- `_makehuman_head` imports the GLB and adds a **skull-conforming hair cap**
+  derived from the closed head shell (scaled shell + boolean front-sphere
+  cut + decimate). Hair skips the old `hair_normal.png` because the skull UVs
+  produced large dark tangent patches.
+- Head faces fully covered by the cap are deleted to recover ~950 triangles;
+  boundary faces stay as a safety band, so the accepted face geometry is
+  untouched. The hidden neck plug uses 12 segments.
+- The procedural body was narrowed at the neck and shoulders (chest 0.158,
+  neck base 0.060, neck top 0.054, shoulder root z 1.345) and its skin decimate
+  dropped to 0.21 so all 12 variants fit the 16,000 cap.
+- Local review renders were removed with the 2026-11-05 `tmp/` cleanup; the
+  committed review sheet above is the retained evidence.
+
+## Deferred polish
+
+- Replace the radial lid mask with real upper/lower lid masses that fold over
+  the globe, with pointed canthi, and pass the profile view.
+- Move the iris onto a curved cornea cap so its orientation follows the globe at
+  three-quarter angles, and use a lighting-driven catchlight instead of baked
+  white geometry.
+- Refine the hair cap silhouette (current short cap reads as a helmet) and
+  improve the full-body shoulder/arm shape before the 12-variant rollout.
+- Add a clean UV/material pass and a contract armature/weights when the head
+  becomes part of the shipped library characters.