feat(client): follow-facing — body commits to path, mouse drives layered head/torso look-at (T-1088)

During an RMB path-follow the body yaw locks to the leg direction (rig
commit_body_to_motion, from interpolated velocity — immune to SetFacing
interleaving between throttled steps). The mouse instead drives a layered
look-at: LookAtModifier3D pair on Head (±70°) + spine_02 (±30° torso twist
for looking far lateral/behind — past their sum the character physically
cannot look further without turning). Forward axis measured from the
armature rest pose (+Z), not guessed. Influence fades in/out on follow
start/end. Pure client presentation per D-249; SetFacing still rides the
wire, so the server vision cone follows the mouse while walking — the
character looks where the player points.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

spikes/synty-intake/scripts/bone_axes_dump.py

@@ -0,0 +1,20 @@
+"""Dump rest-pose local matrices for look-at target bones in armature.glb."""
+import sys
+
+import bpy
+
+glb = sys.argv[sys.argv.index("--") + 1]
+bpy.ops.wm.read_factory_settings(use_empty=True)
+bpy.ops.import_scene.gltf(filepath=glb)
+for obj in bpy.data.objects:
+    if obj.type == "ARMATURE":
+        for name in ("Head", "neck_01", "spine_02", "spine_03"):
+            b = obj.data.bones.get(name)
+            if b is None:
+                print(name, "MISSING")
+                continue
+            # matrix_local: bone rest transform in armature space.
+            m = b.matrix_local
+            print(name, "head:", [round(v, 3) for v in b.head_local])
+            for row in range(3):
+                print("   ", [round(m[row][c], 3) for c in range(4)])