Body step 2.3: view rides the body, mantling and climbing work

- view follows the body (deadzone, smoothed, hard 8 cm limit); no drift over
  six held poses; hanging keeps the view on the character's head
- hold-back measured at the hips, capped leg push while held, stiffer balance
- sticky legs tuck with free-space check (fixes the mantle shove loop)
- strength asymmetric by direction; structural guide strength push-only
- limb/torso friction set before AddChild (Box3D reads it only at creation)
- new phases: pose hold, hang, human-motion mantle, hand-over-hand wall climb

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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