Ship the 47-exercise library in-app: export, fixtures, tests, docs

render.py --export bundles the 25 new motion rigs and info pages;
figure-fixtures.json regenerated for all 47 (the Swift solver reproduces
every new motion, including negative-y pins and the new prop uses). The
fixture count assertion moves to 47, and the no-bundled-motion test now
uses Treadmill - a permanent COVERAGE.md exclusion - since Bench Press
exists. 48 tests green; watch target builds. Coverage handoff complete -
TODO-coverage.md retired.

Claude-Session: https://claude.ai/code/session_01HJDQQDA9QdP8zByg43H5v3

Workouts/Resources/ExerciseMotions/Triceps Pushdown.info.md

@@ -0,0 +1,39 @@
+# Triceps Pushdown
+
+The cable triceps staple — elbows pinned to the sides, push the bar from
+chest height down to straight arms.
+
+- **Category:** Main circuit
+- **Type:** Machine-based cable elbow extension
+- **Targets:** Triceps
+- **Prescription:** 3 × 10–12
+
+## Setup
+
+Stand at the high pulley with a bar or rope attachment, feet under the
+hips, slight forward lean. Grip with the elbows bent past 90° and tucked
+to the ribs.
+
+## Execution
+
+1. Push the handle down until the arms are completely straight.
+2. Squeeze the triceps at the bottom for a beat.
+3. Let the forearms ride back up until they pass 90°, elbows never
+   leaving the sides.
+
+## Cues
+
+- Elbows are bolted to the ribs — only the forearms move.
+- Stand tall-ish; don't lean your bodyweight onto the bar.
+- Full lockout every rep; the last few degrees are the exercise.
+
+## Common Mistakes
+
+- Elbows drifting forward and up on the way down.
+- Shoulders and back pressing the weight instead of the triceps.
+- Cutting the top of the rep short.
+
+## Progression
+
+Add a plate when every rep locks out with quiet elbows; a rope
+attachment adds a harder finish at the bottom.