Fix NPCs walking backwards

Avatars called Godot's look_at(), which points the node's -Z axis at the target,
but the rig's face (eyes/brows/mouth/focus disc, and the Blender successor) is on
+Z. Every walking NPC therefore faced away from its movement direction.

- add the pure yaw_towards(direction) helper (+Z forward) and use it in both
  movement paths and the reaction face-turn
- fix the head-turn offset to the same +Z convention (basis.z)
- test +Z/+X/-Z/arbitrary directions; recapture targeting screenshot
- TODO bug item moved to DONE, MEMORY records the convention

Headless 209/209.

TODO.md

@@ -1,17 +1,13 @@
 # TODO
 
 Godot 4.3 prototype. Latest release **v0.5.0** (NPC characters and player movement). Headless
-suite **208/208** plus **56** Python tooling tests; the session, PLAN-verb, crowd, emergency,
+suite **209/209** plus **56** Python tooling tests; the session, PLAN-verb, crowd, emergency,
 timeline, audio, scenario-content, props, NPC-budget, movement, and windowed focus/radial smokes
 pass. Anonymous downloads are enabled on the host.
 
 The scheduled presentation pass is complete (see `DONE.md`). The next scheduled pass is the
 graphics-quality work in [`docs/plan-graphics-v0.6.md`](docs/plan-graphics-v0.6.md).
 
-## Bug Fix NPCs walking backwards
-
-- [ ] Investigate and fix the issue causing NPCs to walk backwards during movement.
-
 ## Graphics quality — Blender-authored NPC characters (v0.6.0)
 
 Detailed plan: [`docs/plan-graphics-v0.6.md`](docs/plan-graphics-v0.6.md) · [ADR-0013](docs/adr/0013-blender-authored-npc-characters.md)