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.

TODO.md

@@ -27,13 +27,13 @@ Suggested blender skills: **references** (reference-image-match), **archviz**, *
 - [x] Import character into Unreal; validate skeleton, scale, and materials. Done: `/Game/Test/Character` — `SkeletalMesh` (138 bones), `Skeleton`, warm `M_Character_Export` material with baked `T_Character_Diffuse`.
 - [x] Promote the character asset into a reusable NPC prefab (visible body, collision capsule, idle pose) ready for pedestrians (`0.5.0`) once the third-person body lands. Done 2026-11-07: `AGigLineNPCPerson` (see the 0.1.0 Character-development item); `0.5.0` reuses it as the pedestrian base.
 - [x] Create basic idle/walk animation set. Done 2026-11-09: `Tools/character_anim_build.py` authors `GigLine_Idle` (60 f) and `GigLine_Walk` (30 f) at 30 fps from parametric cycles, and `Tools/ue_character_anim_import.py` imports them. Both AnimSequences verified in `/Game/Test/Character`: Idle 1.967 s, Walk 0.967 s. Limb axes were **measured** on the rig, not assumed — the probe rotated `upperleg01.L` 0.5 rad per axis and read `foot.L`, which showed X is the fore/aft swing (Y twists, Z abducts).
-- [A] Verify animation plays correctly on the imported rig. Import-time verification passes (two AnimSequences, correct lengths); **playback on a possessed pawn is not yet verified** — it needs the third-person camera item below, because the demo pawn carries no visible body. Visual confirmation lands with that item.
+- [A] Verify animation plays correctly on the imported rig. **Playback is broken and now measurable**: the pawn's mesh is bound, both clips resolve, and the run logs `GigLine: playing body clip Character_AnimHuman_rig_GigLine_Idle`, but shot 5 still renders the body in bind pose (arms out). So `PlayAnimation` is called and the pose is not applied — next step is to check whether the imported clip carries bone curves at all (the FBX bake may be sampling only keyed bones) or whether the component needs `SetAnimationMode(AnimationSingleNode)` before `SetAnimation`/`Play`.
 
 ### Camera and controls
 
-- [ ] Add third-person camera following the player body.
-- [ ] Add first/third-person toggle.
-- [ ] Add camera collision to prevent clipping through geometry.
+- [x] Add third-person camera following the player body. Done 2026-11-09: `USpringArmComponent` + camera on the capsule, boom 340 cm, lag 8, and the body is the animated skeletal mesh with the skin material. Review shot 5 (`demo-third-person`, `Screenshots/README.md`) shows the rig; the shipped default view stays first person.
+- [x] Add first/third-person toggle. **V**, via `IA_ToggleCamera`; the toggle swaps the active camera and the body's visibility. `-thirdperson` on the command line starts in third person so the review is reproducible.
+- [x] Add camera collision to prevent clipping through geometry. The spring arm's collision test (`bDoCollisionTest`, probe 12 cm on `ECC_Camera`) shortens the boom instead of letting the camera pass through a wall. **Not yet exercised against a wall in a shot** — the spawn point has open space behind it, so this is implemented but unproven.
 - [ ] Document any input changes.
 
 ### Release checks