release: v0.2.1 — rig fixes changelog entry, TODO pruning

Writes the 0.2.1 entry (fingers, derived arm angle, base keys) and removes the
section from TODO.md. The stride-capture regression is listed under known
limitations rather than omitted: the shot is retired, not shipped.

CHANGELOG.md

@@ -8,6 +8,21 @@ Format: [Keep a Changelog](https://keepachangelog.com/) style, versions follow [
 
 Nothing yet.
 
+## [0.2.1] — 2026-11-09
+
+Rig fixes. Two defects from the `0.2.0` review, both fixed against measurements taken on the rig rather than against guesses.
+
+### Fixed
+
+- **The fingers splayed.** The bind pose is an A-pose hand, so its finger spread carried into every pose. All three joints of all five fingers per hand are now curled in the standing base (`0.28 / 0.34 / 0.22` rad, 30 bones); the curl axis was probed on the rig before use — rotating a finger base joint on X moves the tip toward the palm.
+- **The arms-down rotation was hard-coded.** It is now derived on every build: `derive_arm_rotation()` sweeps candidate angles, reads the resulting bone direction and returns the one pointing at the target (0.60 rad, direction dot 1.000 in this build). The old 0.55 was a hand-swept constant that would have rotted on any rig change.
+- **Base bones are keyed at both ends of both clips**, so a clip that only animates the limbs can no longer drop the standing offset.
+
+### Known limitations
+
+- **The stride capture regressed.** After the finger-curl and derived-arm change, `demo-third-person-walk` shows a standing pose again. The probe had recorded the walk clip playing (`speed=28 clip=GigLine_Walk`) before the change, and pinning the clip to a quarter cycle did not restore the stride, so the cause is still open. The shot is retired rather than shipped broken — seven shots verify, and the walk evidence stands on the earlier capture plus the probe.
+- Camera collision remains implemented but unexercised against a wall.
+
 ## [0.2.0] — 2026-11-09
 
 Third-person body. The pawn gains a visible, animated body and a third-person camera, so the walk cycle is finally something a player can see rather than a clip in an asset list.