fix(cloth): solve the garment instead of repairing it five times

The skirt glitched when the character moved and the thigh still came
through it. Both came from the same place: the solver integrated one
spring per bone and then ran four more passes behind it — resolve the
collision against the target, resolve it again against the answer, relax
the cross-panel links and rebuild every pose from the corrected tips,
then walk a separate ancestor "lift" — each writing bone poses the next
read back and partly undid. The lift wrote poses that were never fed back
into the spring state at all, so every frame began by pulling against a
pose the springs did not know about.

Replaced with one position-based solve, the shape Magica Cloth 2's
BoneCloth uses. Every JOINT is a particle, so a bone's head can move;
predict with inertia in the anchor's frame; relax length, bend, backstop,
the cross-panel links and the colliders together; convert to rotations
once at the end. A contact with no rotational leverage is now resolved by
the panel moving, which is what a bodily chain push, an ancestor lift and
a drape weight were each approximating separately.

Measured, at a dead-still idle and over a movement sweep:

  idle jitter (skirt)      0.53 -> 0.025 deg/frame, worst 24 -> 1.9
  settling after a dash    103 -> 18 mm of leg left inside the skirt
  fall / air / walk         82 -> 40, 96 -> 75, 72 -> 76 mm
  run / slide / dash        unchanged, ~95 mm

The idle buzz and the failure to come home after a hard move are gone —
those were the "glitches out". Peak clipping in a run, a slide and a dash
is NOT fixed and is still around 95 mm.

Four things this turned up on the way:

- debug/cloth_clip_check.gd was measuring the animation, not the render.
  Godot restores bone poses after the modifier pass, so reading them with
  force_update_all_bone_transforms() afterwards sees nothing any modifier
  did. It reported the same ~95 mm with collision fully enabled and with
  it commented out. It now observes from inside the pass. Every number
  ever taken from this tool before now was measuring the wrong pose.

- The collision hulls came from ten farthest-point samples per bone,
  which describe a panel's corners and hem and leave its MIDDLE unsampled
  — exactly where a thigh comes through. Built from the real mesh at load
  time instead.

- The drape term is gone. It was there to move a panel the old solver
  could not, and once the solver could, it was worse in every state but a
  walk and cost 20x in stability: its target sat inside the leg the
  collision was pushing out of, so the two ran against each other forever.

- Cost was 10.9 ms per character. The inner loop rebuilt every capsule
  and reallocated the hull array for every (bone, collider, pass). Now
  2.6 ms at full quality with a distance LOD behind it.

Co-Authored-By: Claude Opus 5 <[email protected]>

debug/skirt_run_view.gd.uid

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