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.

tools/test_npc_pipeline.py

@@ -0,0 +1,44 @@
+import os
+import unittest
+from pathlib import Path
+
+import npc_pipeline
+
+
+class NpcContractTests(unittest.TestCase):
+    def test_contract_constants(self):
+        self.assertEqual(npc_pipeline.SLOTS,
+                         ["skin", "cloth", "pants", "accessory", "hair"])
+        for bone in ["Head", "HipL", "HipR", "KneeL", "KneeR",
+                     "ShoulderL", "ShoulderR", "ElbowL", "ElbowR",
+                     "HandL", "HandR"]:
+            self.assertIn(bone, npc_pipeline.BONES)
+        self.assertLessEqual(npc_pipeline.MAX_TRIANGLES, 6000)
+        self.assertLessEqual(npc_pipeline.MAX_VERTICES, 4000)
+
+    def test_textures_exist_for_every_slot(self):
+        for slot in npc_pipeline.SLOTS:
+            for suffix in ("albedo", "normal", "orm"):
+                path = npc_pipeline.TEX_DIR / f"{slot}_{suffix}.png"
+                self.assertTrue(path.is_file(), path)
+                self.assertGreater(path.stat().st_size, 100, path)
+
+    @unittest.skipUnless(npc_pipeline.GLB_PATH.is_file(), "npc_base.glb not built")
+    def test_committed_model_audits_clean(self):
+        result = npc_pipeline.audit_glb()
+        self.assertTrue(result["ok"], result["issues"])
+        self.assertLessEqual(result["triangles"], npc_pipeline.MAX_TRIANGLES)
+        self.assertLessEqual(result["vertices"], npc_pipeline.MAX_VERTICES)
+        for bone in npc_pipeline.BONES:
+            self.assertIn(bone, result["bones"])
+
+    @unittest.skipUnless(npc_pipeline.GLB_PATH.is_file(), "npc_base.glb not built")
+    def test_blend_source_is_committed(self):
+        self.assertTrue(npc_pipeline.BLEND_PATH.is_file())
+        # Godot must not try to import the .blend (it hangs without Blender).
+        gdignore = npc_pipeline.BLEND_PATH.parent / ".gdignore"
+        self.assertTrue(gdignore.is_file(), "assets/models/npc/.gdignore is required")
+
+
+if __name__ == "__main__":
+    unittest.main()