Surface machine settings in the exercise library and refine machine rigs

Library detail screens now lead with the user's recorded machine settings
(per-split when they disagree, empty-state card for machine-based entries)
and append the weight progression chart. Starter seeds mark machine
exercises with an empty machineSettings list so the settings UI lights up
before first use. The figure rig gains a frontal body profile for face-on
machines, props that can ride mid joints (knees/elbows), and an
alternating four-frame Bird Dog loop.

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

WorkoutsTests/ExerciseMotionTests.swift

@@ -11,8 +11,10 @@ struct ExerciseMotionTests {
     @Test func bundledBirdDogResourcesDecode() throws {
         let resources = try #require(ExerciseMotionLibrary.resources(for: "Bird Dog"))
         #expect(resources.motion.name == "Bird Dog")
-        #expect(resources.motion.frames.count == 2)
-        #expect(resources.motion.working == ["arm_r", "leg_l"])
+        // Bird Dog alternates sides, so all four limbs are in the working set and
+        // the loop is four key frames (lift right/left pair, then the opposite pair).
+        #expect(resources.motion.frames.count == 4)
+        #expect(resources.motion.working == ["arm_r", "leg_l", "arm_l", "leg_r"])
         #expect(resources.body.upperArm == 30)
         #expect(MotionTimeline(motion: resources.motion, body: resources.body) != nil)
     }