Load and animate the Blender-authored NPC base mesh

Wire the skinned model from ADR-0013 into NpcAvatar:

- _build_skinned_body() instantiates the imported npc_base.glb, binds the 14
  armature bones, and keeps the procedural _build_body() as the offline
  fallback (use_skinned_model can force it in tests)
- outfit_for()/layer_for() tint the five material slots through the new
  SurfaceMaterials.npc_slot(); accessories and hand items attach under Rig/Head
- the existing limb pivots (Hip/Knee/Shoulder/Elbow/Hand + Head marker) keep the
  old animation math; _sync_skeleton() copies their rotations to bones. Bone
  pose rotation is absolute local orientation, so it is composed with the rest
  basis (otherwise the whole body snaps into a broken pose)
- skinned rigs scale uniformly (non-uniform parent scale shears the skin) and
  keep Rig/Head for the focus cone, nametag, and reaction tag
- commit the editable npc_base.blend plus a .gdignore: Godot's editor otherwise
  tries to import the blend and hangs during --import
- npc_pipeline audit tests (contract, textures, clean GLB, committed source)

Verification: headless 212/212, Python tooling 60/60, NPC budget 16 avatars =
144 meshes at ~6.9 ms, movement/focus/props smokes pass, compare 11 good / 0 bad.
TODO Phases 0-3 checked; environment lift and release remain.

README.md

@@ -226,8 +226,10 @@ tonemapping, glow, fog, colour grading) that the phase lighting applies.
 NPCs are moving from the procedural capsule rig to a skinned, UV-mapped base
 character authored in Blender ([ADR-0013](docs/adr/0013-blender-authored-npc-characters.md)).
 `tools/npc_pipeline.py` builds `assets/models/generated/npc_base.glb` plus the
-per-slot material maps, and `NpcAvatar` keeps the procedural rig as the offline
-fallback until the model is wired in (see the [graphics plan](docs/plan-graphics-v0.6.md)).
+per-slot material maps. `NpcAvatar` instantiates that skinned model, tints its
+five material slots from the seed-driven outfit, and drives the bones from the
+existing animation code; the procedural rig remains the offline fallback (see
+the [graphics plan](docs/plan-graphics-v0.6.md)).
 
 ```bash
 # Print the frozen contract (slots, bone names, triangle budget)