Give the figure real girdles, fix orbit pinning, add roller pads

Shoulder and pelvis widths grow to human-like proportions per profile
(shoulders wider than hips for neutral/male, reversed for female) and
are now drawn — bars across the attach points that read near-full-width
face-on and as a shoulder/hip nub in profile, so limbs visibly hang
from a torso instead of a point. Orbiting no longer re-solves IK pins
in the rotated view (pins are canvas targets in the authored camera):
the pose resolves first and the posed body rotates, which fixes hands
sticking to stale screen points mid-orbit (Cat-Cow, Bird Dog, Plank).
Leg Extension and Leg Curl swap their ankle bars for a machine roller
disc — a new `roller` prop riding the shin's press side. Fixtures
regenerated; both renderers updated in lockstep.

Claude-Session: https://claude.ai/code/session_01LEoff8bXGBS83tK1c55Mf7

Workouts/ExerciseFigure/ExerciseMotion.swift

@@ -159,7 +159,7 @@ struct PropSceneShape: Codable {
 /// One equipment prop. `type` selects the flavor; the other fields apply per type
 /// (mirroring the reference renderer's `resolve_props`).
 struct MotionProp: Codable {
-    let type: String          // "scene" | "cable" | "bar" | "dumbbell" | "pad"
+    let type: String          // "scene" | "cable" | "bar" | "dumbbell" | "pad" | "roller"
     /// scene: the static shapes.
     let shapes: [PropSceneShape]?
     /// cable: fixed anchor `[x, y]` → moving joint `to`.
@@ -174,6 +174,11 @@ struct MotionProp: Codable {
     let w: Double?
     /// End-disc radius (dumbbell plates default 4.5; bars none).
     let plateR: Double?
+    /// roller: which side of the lower bone the disc presses (+1/−1), its radius,
+    /// and how far back along the bone from the joint it sits.
+    let side: Double?
+    let r: Double?
+    let back: Double?
 }
 
 /// A key frame of anatomical joint angles. A joint absent from the frame poses at