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/Lat Pull Down/frames/frame-1.svg

@@ -12,7 +12,7 @@
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   <path id="leg_r" d="M 150.0 123.2 L 194.4 111.4 L 193.0 150.8 L 204.0 151.2" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 147.7 40.3 L 174.8 27.4 L 194.0 4.7" stroke="#0d9488" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M 172.0 3.8 L 220.0 3.8" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M 196.0 -0.3 L 196.0 8.0" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
   <circle id="head" cx="149.5" cy="18.7" r="10" fill="white" stroke="#3a3f4b" stroke-width="6"/>
   <line id="nose" x1="155.3" y1="10.6" x2="159.3" y2="4.9" stroke="#3a3f4b" stroke-width="4" stroke-linecap="round"/>
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Exercise Library/Lat Pull Down/frames/frame-2.svg

@@ -12,7 +12,7 @@
   <path id="spine" d="M 150.0 122.0 Q 146.6 79.2 147.7 38.3" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="leg_r" d="M 150.0 123.2 L 194.4 111.4 L 193.0 150.8 L 204.0 151.2" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 147.7 40.3 L 171.7 58.0 L 194.0 38.2" stroke="#0d9488" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M 172.0 37.3 L 220.0 37.3" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M 196.0 33.2 L 196.0 41.5" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
   <circle id="head" cx="149.5" cy="18.7" r="10" fill="white" stroke="#3a3f4b" stroke-width="6"/>
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Exercise Library/Lat Pull Down/motion.json

@@ -9,7 +9,7 @@
       {"kind": "circle", "c": [272, 19], "r": 4, "fill": true, "color": "prop"}
     ]},
     {"type": "cable", "from": [272, 19], "to": ["hand_r", "hand_l"], "w": 4},
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 24}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 24}
   ],
   "frames": [
     {

Exercise Library/Lat Pull Down/visual.svg

@@ -12,7 +12,7 @@
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   <path id="leg_r" d="M 150.0 123.2 L 194.4 111.4 L 193.0 150.8 L 204.0 151.2" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 147.7 40.3 L 171.7 58.0 L 194.0 38.2" stroke="#0d9488" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M 172.0 37.3 L 220.0 37.3" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M 196.0 33.2 L 196.0 41.5" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
   <circle id="head" cx="149.5" cy="18.7" r="10" fill="white" stroke="#3a3f4b" stroke-width="6"/>
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