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/Bench Press/frames/frame-1.svg

@@ -11,9 +11,9 @@
   <path id="spine" d="M 150.0 116.0 Q 106.5 116.0 65.0 116.0" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="leg_r" d="M 150.0 117.2 L 195.3 109.3 L 196.0 148.7 L 206.9 147.6" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 65.0 117.9 L 91.6 131.7 L 93.0 102.2" stroke="#0d9488" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M 69.0 101.2 L 121.0 101.2" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
-  <circle cx="69.0" cy="101.2" r="12" fill="#6b7180"/>
-  <circle cx="121.0" cy="101.2" r="12" fill="#6b7180"/>
+  <path d="M 95.0 96.7 L 95.0 105.8" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <circle cx="95.0" cy="96.7" r="12" fill="#6b7180"/>
+  <circle cx="95.0" cy="105.8" r="12" fill="#6b7180"/>
   <circle id="head" cx="45.2" cy="113.3" r="10" fill="white" stroke="#3a3f4b" stroke-width="6"/>
   <line id="nose" x1="46.6" y1="103.4" x2="47.6" y2="96.5" stroke="#3a3f4b" stroke-width="4" stroke-linecap="round"/>
   <g font-family="-apple-system, Helvetica, sans-serif" font-size="11" fill="#6b7180">

Exercise Library/Bench Press/frames/frame-2.svg

@@ -11,9 +11,9 @@
   <path id="spine" d="M 150.0 116.0 Q 106.5 116.0 65.0 116.0" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="leg_r" d="M 150.0 117.2 L 195.3 109.3 L 196.0 148.7 L 206.9 147.6" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 65.0 117.9 L 60.6 88.7 L 67.0 59.8" stroke="#0d9488" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M 43.0 58.9 L 95.0 58.9" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
-  <circle cx="43.0" cy="58.9" r="12" fill="#6b7180"/>
-  <circle cx="95.0" cy="58.9" r="12" fill="#6b7180"/>
+  <path d="M 69.0 54.4 L 69.0 63.4" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <circle cx="69.0" cy="54.4" r="12" fill="#6b7180"/>
+  <circle cx="69.0" cy="63.4" r="12" fill="#6b7180"/>
   <circle id="head" cx="45.2" cy="113.3" r="10" fill="white" stroke="#3a3f4b" stroke-width="6"/>
   <line id="nose" x1="46.6" y1="103.4" x2="47.6" y2="96.5" stroke="#3a3f4b" stroke-width="4" stroke-linecap="round"/>
   <g font-family="-apple-system, Helvetica, sans-serif" font-size="11" fill="#6b7180">

Exercise Library/Bench Press/motion.json

@@ -8,7 +8,7 @@
       {"kind": "line", "pts": [[78, 129], [78, 150]], "w": 4},
       {"kind": "line", "pts": [[144, 129], [144, 150]], "w": 4}
     ]},
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 12}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 12}
   ],
   "frames": [
     {

Exercise Library/Bench Press/visual.svg

@@ -11,9 +11,9 @@
   <path id="spine" d="M 150.0 116.0 Q 106.5 116.0 65.0 116.0" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="leg_r" d="M 150.0 117.2 L 195.3 109.3 L 196.0 148.7 L 206.9 147.6" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
   <path id="arm_r" d="M 65.0 117.9 L 91.6 131.7 L 93.0 102.2" stroke="#0d9488" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M 69.0 101.2 L 121.0 101.2" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
-  <circle cx="69.0" cy="101.2" r="12" fill="#6b7180"/>
-  <circle cx="121.0" cy="101.2" r="12" fill="#6b7180"/>
+  <path d="M 95.0 96.7 L 95.0 105.8" stroke="#6b7180" stroke-width="4" stroke-linecap="round" stroke-linejoin="round"/>
+  <circle cx="95.0" cy="96.7" r="12" fill="#6b7180"/>
+  <circle cx="95.0" cy="105.8" r="12" fill="#6b7180"/>
   <circle id="head" cx="45.2" cy="113.3" r="10" fill="white" stroke="#3a3f4b" stroke-width="6"/>
   <line id="nose" x1="46.6" y1="103.4" x2="47.6" y2="96.5" stroke="#3a3f4b" stroke-width="4" stroke-linecap="round"/>
   <g font-family="-apple-system, Helvetica, sans-serif" font-size="11" fill="#6b7180">