Give cross-body bars a true 3D axis and fix the goblet squat hold

The orbit was always a real camera orbit — figure and props share one
rigid rotation — but a bar's screen-space angle authored the wrong 3D
rod: the default horizontal encoded a rod along the body axis, so
barbells hovered fixed on screen and vanished at the head-on view
where they should span widest. Line props now take "axis": "z" (both
renderers in lockstep, fixture-pinned): the world left-right direction
projects through the camera pitch like the floor quad — end-on plates
in profile, full span face-on, swinging with the hands in between.
Applied to the ten cross-body bars; vertical handles were already
orbit-invariant.

Goblet Squat's hand pins sat so close to the shoulders that the
two-bone IK was degenerate, flipping between a chicken-wing and an
elbow-behind solve; re-pinned level with the shoulders so the elbows
tuck straight down through the whole rep.

Claude-Session: https://claude.ai/code/session_01HJDQQDA9QdP8zByg43H5v3

Exercise Library/Deadlift/frames/frame-1.svg

@@ -8,9 +8,9 @@
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   <path id="spine" d="M 112.4 108.6 Q 142.6 103.8 169.8 93.5" stroke="#0d9488" stroke-width="4.2" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 169.8 94.8 L 164.3 114.8 L 158.1 134.6" stroke="#3a3f4b" stroke-width="4.2" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M 141.4 133.7 L 177.8 133.7" stroke="#6b7180" stroke-width="2.8" stroke-linecap="round" stroke-linejoin="round"/>
-  <circle cx="141.4" cy="133.7" r="11.2" fill="#6b7180"/>
-  <circle cx="177.8" cy="133.7" r="11.2" fill="#6b7180"/>
+  <path d="M 159.6 130.6 L 159.6 136.9" stroke="#6b7180" stroke-width="2.8" stroke-linecap="round" stroke-linejoin="round"/>
+  <circle cx="159.6" cy="130.6" r="11.2" fill="#6b7180"/>
+  <circle cx="159.6" cy="136.9" r="11.2" fill="#6b7180"/>
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Exercise Library/Deadlift/frames/frame-2.svg

@@ -8,9 +8,9 @@
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   <path id="spine" d="M 153.0 90.4 Q 158.3 60.9 163.3 32.7" stroke="#0d9488" stroke-width="4.2" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 163.3 34.0 L 167.6 54.3 L 160.7 73.8" stroke="#3a3f4b" stroke-width="4.2" stroke-linecap="round" stroke-linejoin="round"/>
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-  <circle cx="143.9" cy="73.2" r="11.2" fill="#6b7180"/>
-  <circle cx="180.3" cy="73.2" r="11.2" fill="#6b7180"/>
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Exercise Library/Deadlift/motion.json

@@ -4,7 +4,7 @@
   "camera": {"zoom": 0.7},
   "working": ["leg_r", "leg_l", "spine"],
   "props": [
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 16}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 16}
   ],
   "frames": [
     {

Exercise Library/Deadlift/visual.svg

@@ -8,9 +8,9 @@
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   <path id="spine" d="M 112.4 108.6 Q 142.6 103.8 169.8 93.5" stroke="#0d9488" stroke-width="4.2" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 169.8 94.8 L 164.3 114.8 L 158.1 134.6" stroke="#3a3f4b" stroke-width="4.2" stroke-linecap="round" stroke-linejoin="round"/>
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-  <circle cx="141.4" cy="133.7" r="11.2" fill="#6b7180"/>
-  <circle cx="177.8" cy="133.7" r="11.2" fill="#6b7180"/>
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+  <circle cx="159.6" cy="130.6" r="11.2" fill="#6b7180"/>
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   <circle id="head" cx="183.4" cy="90.4" r="7.0" fill="white" stroke="#3a3f4b" stroke-width="4.2"/>
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