feat(camera): third-person rig, V toggle, visible body

One pawn, both rigs (ADR-9): a skeletal body hidden in first person, a
collision-tested spring arm, and a toggle that swaps the active camera and the
body's visibility. Shipped default stays first person; -thirdperson starts the
pawn in the third-person rig so the review shot is reproducible, and the
screenshot run passes it.

Three defects found and two fixed:
- The skin material had no SkeletalMesh usage flag, so Unreal silently substituted
  the default grey. That is why the body rendered as clay.
- render_screenshots.sh still called ./Engine/... on this branch (the fix lives on
  the facade branch and never reached main); applied here so the shots generate.
- OPEN: the idle clip is bound and PlayAnimation is called - the run logs the clip
  name - but the body still renders in bind pose, arms out. Recorded with that
  evidence in TODO.md rather than called done.

Shot 5 (demo-third-person) added and documented; camera collision is implemented
but unproven, since the spawn has open space behind it.

Tools/ue_build_review_map.py

@@ -308,6 +308,11 @@ try:
             # (X -22750) and look NORTH toward the mass. The old camera was at
             # X -22800 Y +2600 aiming at its own X, giving an 85%-sky frame.
             ("demo-north-buildings", unreal.Vector(-22750, 1600, 500), unreal.Vector(-22750, -5200, 350)),
+            # 0.2.0 third-person body. Stands where the pawn's own boom camera sits —
+            # 3.4 m behind the spawn point, 1 m above it — and looks at the pawn, so
+            # the visible body and its idle clip are what the shot is for.
+            # Demo_PlayerStart is at (-13336, -1150, 600), yaw 90 (facing +Y).
+            ("demo-third-person", unreal.Vector(-13336, -1750, 780), unreal.Vector(-13336, -1150, 560), 58.0),
         ]
         seq = spawn(unreal.GigLineShotActor, unreal.Vector(0, 0, 300), "ShotSequencer")
         if seq: