fix(rig): curl the fingers, derive the arm angle

Two defects from the 0.2.0 review, both fixed and both measured.

- Fingers splayed because the bind is an A-pose hand. All three joints of all five
  fingers per hand are curled in the standing base (0.28/0.34/0.22 rad), with the
  curl axis probed on the rig first. The front shot now shows relaxed hands.
- The arms-down rotation is derived on every build instead of hard-coded: the
  builder sweeps candidate angles and returns the one whose bone direction points at
  the target (0.60 rad, direction dot 1.000 this build). The old 0.55 was a
  hand-swept constant.
- Base bones are keyed in both clips, so a clip that only animates the limbs cannot
  drop the standing offset.

Regression, recorded rather than hidden: the stride shot shows a standing pose again
after this change. The probe had shown the walk clip playing (speed=28
clip=GigLine_Walk) before it, and pinning the clip to a quarter cycle did not restore
the stride, so the cause needs a fresh look. The shot is retired rather than shipped
broken, and the known-issues table now points at it.

Screenshots/README.md

@@ -130,19 +130,6 @@ What it shows: the arms hang down with a soft elbow bend, the hands sit at hip h
 
 ---
 
-## 8. Third-person walk
-
-![Third-person walk: the body mid-stride in profile](demo/review-demo-third-person-walk.png)
-
-- **File:** `demo/review-demo-third-person-walk.png`
-- **View:** tracking camera, 4.2 m to the pawn's right, captured while the pawn walks south under `-walk`
-- **Expected content:** the body mid-stride in profile — legs apart, arms counter-swinging
-- **Verified:** ☑ 2026-11-09 · **Approved:** ☐ pending
-
-**Why it needed new harness:** a fixed camera cannot photograph a pawn moving at 4.5 m/s. Three attempts framed it differently every run and two missed it entirely. The shot actor now has a per-shot `ShotFollow` mode that re-places the camera every frame at a fixed offset in the pawn's frame, and the walk is driven per shot, so the capture is deterministic.
-
-**What it proves:** the walk clip plays and advances. The earlier captures of this shot showed one frozen pose because the sequencer's `BeginPlay` ran before the player pawn existed, so the cast that enables walking silently found nothing and `speed` stayed at zero — the probe read `walk=0 speed=0 clip=Idle` every frame. Moving that call into the per-frame follow update fixed it; the capture now logs `walk=1 speed=28 clip=GigLine_Walk` and shows a stride.
-
 ---
 
 ## The iteration loop (uncommitted)
@@ -174,7 +161,7 @@ Every issue is tracked in `TODO.md` under the version that will fix it; an issue
 | Nothing may stand in front of the hero façade that blocks it — no awning, no temporary structure | `0.9.0` → per-building models, hero façade | Open |
 | Retail parapet has no moulded profile, and wall lettering built as a plate does not read at 40 m | `0.9.0` → 6800 Lee Drug and 6806–6820, second pass | Open (moved out of `0.1.6`) |
 | 6822 Budget is a bare blockout volume — no photograph exists to model it from | `0.9.0` → photography gap | Deferred (moved out of `0.1.6`) |
-| Third-person fingers splay rather than relax — the bind's finger spread is carried into the pose | `0.2.2` → skin and animation tuning | Open |
+| The stride shot shows a standing pose again since the finger-curl and derived-arm change; the walk clip plays (`speed=28 clip=GigLine_Walk` in the probe) but the capture lands on a still | `0.2.3` → camera and capture fixes | Open |
 | Camera collision is implemented but never exercised against a wall | `0.2.0` → camera collision | Open |
 | The walk clip has never been captured in motion — it imports and its curves carry the stride, but no shot shows it | `0.2.0` → verify animation plays correctly | Open |
 | Between kerb and building line the walkable surface is the terrain mesh, not a modelled pavement | `0.6.0` → model the pavement between kerb and building line | Open |