Add the hair part library and give the roster three silhouettes

TODO.md

@@ -766,8 +766,16 @@ regressing gear fit, budget or readability.
       casual/coat/hoodie/crowd_c, casual tee for jacket/dress/crowd_a/crowd_b, worker for
       vest/firefighter/guard/crowd_d. `npc_firefighter`, `npc_guard` and `npc_crowd_d` drop the
       upstream hivis vest and hard hat. All twelve built, AO-baked and committed (`a6ccd86`).
-- [ ] Add the modular part library (hair styles, outfits) so the roster regains the silhouette
-      variety the twelve procedural meshes had; three shared meshes is the current ceiling.
+- [x] **Hair part library.** Every base ships one hair shell; `QUATERNIUS_HAIR_PARTS` reshapes it in
+      place (`short` identity, `buzz` squashed toward the hairline, `long` stretched from the crown),
+      and each role picks a style through the existing `CHARACTERS[...]["hair"]` field. The T-pose
+      cache is keyed on the style. The roster now reads as three silhouettes instead of one.
+- [ ] **Outfit part library.** Unchanged ceiling: three outfit meshes for twelve roles. The upstream
+      modular pack is distributed as a Google Drive folder
+      (<https://drive.google.com/drive/folders/1USAAquX2JJWuA2m6zol0KUkFe3UkZ8zX>), which cannot be
+      fetched reproducibly by a script, so outfit variety needs either a manual intake of that pack
+      (with the CC0 licence + SHA-256 record) or new garments authored here. Decide which before
+      starting; a `bald` hair variant also needs a skull-covering crown on the `worker` base first.
 - [ ] Bake per-slot albedo/normal/ORM maps and a per-slot atlas; the five slots currently share one
       whole-body UV set, which caps how much the cloth/pants tints can differ.