Add the exercise reference library, animated exercise figures, and exercise categories

Exercise Library/ holds per-exercise reference docs (setup, cues,
mistakes, progressions) with SVG visuals and a Python-rendered motion
pipeline; Workouts/ExerciseFigure renders the bundled *.motion.json
rigs as animated stick figures on the exercise screen. Exercises gain
a warm-up/main-circuit category, timed exercises display hold time via
planSummary, and a completed exercise reopens to a check screen instead
of its timers.

Exercise Library/Dead Bug/info.md

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+# Dead Bug
+
+Anti-extension drill — the limbs move while the trunk stays perfectly still.
+
+- **Category:** Warm-up
+- **Type:** Anti-extension
+- **Targets:** Deep core (transverse abdominis), hip flexor control
+- **Prescription:** 8 per side, slow and controlled
+
+## Setup
+
+Lie on your back. Arms straight up over the shoulders, hips and knees bent to
+90°, lower back pressed into the floor.
+
+## Execution
+
+1. Brace and exhale as you lower one arm overhead and the *opposite* leg toward
+   the floor.
+2. Stop just before the lower back peels off the floor.
+3. Return under control and switch sides.
+
+## Cues
+
+- Lower back glued to the floor the entire time — that contact *is* the exercise.
+- Slow negatives; the reach out should take 2–3 seconds.
+- Ribs down, no flaring as the arm goes overhead.
+
+## Common Mistakes
+
+- Arching the lower back as the leg lowers.
+- Moving arm and leg on the same side.
+- Rushing reps and turning it into a flutter kick.
+
+## Progression
+
+Heels sliding on floor → bent-knee reach → straight-leg reach → both legs
+lowering together → light weight held overhead