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.

.gitignore

@@ -47,7 +47,13 @@ build/
 
 # AI / asset-development outputs (regenerated by the tools; not shipped in the game)
 assets/models/concepts/
-assets/models/npc/
+assets/models/npc/*.blend1
 assets/textures/npc/ai/
 assets/textures/ai/*
-!assets/textures/ai/game_ready/
+!assets/textures/ai/game_ready/
+# Godot extracts embedded glTF textures next to the source on import
+assets/models/generated/npc_base_*_albedo.png
+assets/models/generated/npc_base_*_normal.png
+
+# Local AppImage extraction
+squashfs-root/