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/render_screenshots.sh

@@ -39,6 +39,14 @@ run_cmdlet ue_build_review_map.py "5/6 stage the demo shot cameras"
 tail -3 /tmp/ue-review-map-result.txt 2>/dev/null || true
 
 echo "== 6/6 capture the demo map =="
+# Clear the engine's screenshot folder first. The collect step below copies every
+# review-*.png it finds in Saved/, so without this a shot retired from the camera list
+# keeps coming back as a stale file - that is how a removed walk shot reappeared with
+# byte-identical content after a run that never captured it.
+rm -rf "$REPO"/Game/GigLine/Saved/Screenshots/* "$HOME"/.config/Epic/GigLine/Saved/Screenshots/* 2>/dev/null || true
+# Recreate the folder: the engine writes into it and does not recreate a deleted
+# directory, which silently produced zero captures in the run that removed it.
+mkdir -p "$REPO/Game/GigLine/Saved/Screenshots/LinuxEditor"
 # The engine path is absolute: this step runs from the repo, not from $ENGINE, and a
 # bare ./Engine/... failed with "No such file or directory" while every commandlet
 # above succeeded through run_cmdlet's cd.