Slowly orbit the camera around prop-free form guides

Bodyweight motions (no equipment layer, no hide list) now turn the
camera a full revolution every 24 seconds while the motion loops, so
the exercise reads from every side; machine exercises keep their
authored view, since scene equipment is a view-locked billboard and a
hide list describes a single viewpoint.

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

Workouts/ExerciseFigure/ExerciseFigureView.swift

@@ -38,10 +38,19 @@ struct FigureAnimation {
         self.props = resources.motion.props ?? []
     }
 
+    /// Seconds per full camera revolution for orbiting motions.
+    private static let orbitPeriod: Double = 24
+
+    /// Prop-free, hide-free motions slowly orbit the camera while animating — the
+    /// bodyweight moves. Scene equipment is a view-locked billboard and a `hide` list
+    /// describes one authored viewpoint, so machines keep their fixed camera.
+    var orbits: Bool { props.isEmpty && hide.isEmpty }
+
     /// Drawable geometry at `time`, with limbs listed in `hide` dropped so neither they
     /// nor any prop riding them are drawn.
     func geometry(at time: Double) -> FigureGeometry {
-        var geo = timeline.geometry(at: time)
+        let yaw = orbits ? 360 * (time / Self.orbitPeriod) : 0
+        var geo = timeline.geometry(at: time, yawOffset: yaw)
         for name in hide {
             if let limb = FigureLimb(rawValue: name) { geo.limbs[limb] = nil }
         }