Author the machine exercise circuit with props and corrected hip machine motions

Fourteen Planet Fitness machine exercises join the rig library, each with
authored motion, info page, and schematic equipment via the new props layer
(scene shapes, cables, bars, pads) rendered in lockstep by render.py and the
in-app figure renderer. Abductor and Adductor are authored face-on with the
real seated machine motion — knees-bent legs swinging apart/together against
knee pads — replacing the earlier middle-split depiction. The watch target
now bundles the figure renderer and motion rigs too.

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

Workouts/Resources/ExerciseMotions/Plank.info.md

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+# Plank
+
+The baseline anti-extension hold — a rigid line from head to heels.
+
+- **Category:** Main circuit
+- **Type:** Anti-extension (isometric hold)
+- **Targets:** Rectus abdominis, deep core, glutes, shoulders
+- **Prescription:** 3 × 30–60 s holds
+
+## Setup
+
+Forearms on the floor, elbows under shoulders, feet together behind you. One
+straight line from the back of the head to the heels.
+
+## Execution
+
+1. Squeeze glutes and quads hard, tuck ribs down toward the pelvis.
+2. Press the floor away through the forearms — no sagging between the shoulders.
+3. Breathe shallowly behind the brace and hold.
+
+## Cues
+
+- Glutes and quads *tight* — a plank fails at the hips first.
+- Ribs down: think "short front, long back".
+- If the hips sag or the lower back takes over, the set is done.
+
+## Common Mistakes
+
+- Hips sagging (lower back extension — the exact thing to resist).
+- Hips piked high to make the hold easier.
+- Holding the breath entirely.
+
+## Progression
+
+Knee plank → full plank → feet elevated → RKC plank (maximum-tension, shorter
+holds) → weighted plank