feat(review): deterministic walking capture, and the defect it exposed

The shot actor can now photograph a moving pawn: a per-shot ShotFollow flag re-places
the camera every frame at a fixed offset in the pawn's frame, and the walk is driven
per shot (SetReviewWalk) with the pawn returned to spawn after a follow shot, so the
fixed-camera shots later in the list still find it in place. With that, the capture
stopped depending on where a 4.5 m/s pawn happened to be.

Two further bugs fixed on the way:
- the engine's screenshot folder is cleared before each run. The collect step copies
  every review-*.png it finds in Saved/, so a shot retired from the camera list kept
  reappearing with byte-identical content from an older run - which is how a walk shot
  that was never captured looked like a captured one.
- UpdateBodyAnimation no longer calls SetAnimation every frame. Re-setting the same
  clip restarts it, which freezes the body on frame 0.

What the deterministic capture then exposed: the walk clip is applied but does not
advance - every walking frame shows the same pose (arms forward, legs together). The
stride shot is retired again rather than shipped, and TODO.md names the next step:
log GetCurrentAssetTime across frames and check the imported PlayRate. The harness
stays wired for when the clip plays.

Shots 6 and 7 were re-rendered after these changes and still pass; 7/7 verify.

Tools/ue_build_review_map.py

@@ -331,6 +331,10 @@ try:
             seq.set_editor_property("shot_rotations",
                                     [unreal.MathLibrary.find_look_at_rotation(c[1], c[2]) for c in demo_shots])
             seq.set_editor_property("shot_names", [c[0] for c in demo_shots])
+            # No follow shots in the current list: the stride capture was retired
+            # because the walk clip does not visibly advance in game (see TODO.md).
+            # The follow flag stays wired for when it does.
+            seq.set_editor_property("shot_follow", [False] * len(demo_shots))
             seq.set_editor_property(
                 "shot_field_of_view",
                 [float(c[3]) if len(c) > 3 else 0.0 for c in demo_shots])