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.

MEMORY.md

@@ -20,6 +20,12 @@ Session memory for durable decisions, state, and gotchas. Keep concise, remove o
 - Shift length is the scenario's `shift_duration_s` (900 s in all three venues). Tests and the screenshot tool override elapsed time; they do not change the default.
 - RNG: NPC reactions and event scheduling are seedable for deterministic tests.
 
+- **NPC facing (fixed after v0.5.0):** the avatar's visual front is **+Z** (procedural eyes
+  and the Blender model's face). Godot `look_at()` aims **-Z**, which made every NPC walk
+  backwards. Use `NpcAvatar.yaw_towards(dir)` and set `rotation.y`; do not call `look_at()` on
+  avatars. Head-turn offsets use `+basis.z` for the same reason. Covered by
+  `test_yaw_faces_the_movement_direction`.
+
 ## Handoff (read this first)
 
 - **Phase 2 — AI texturing (this agent, DONE 2026-11-01).** Phase 1 assets were