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/Leg Raises/info.md

@@ -0,0 +1,37 @@
+# Leg Raises
+
+Lower-ab builder — the slow lowering is the exercise.
+
+- **Category:** Main circuit
+- **Type:** Anti-extension (dynamic)
+- **Targets:** Lower rectus abdominis, hip flexors, deep core
+- **Prescription:** 3 × 8–15 reps, slow negatives
+
+## Setup
+
+**Lying:** flat on your back, legs straight, hands at your sides (or under the
+tailbone to start). **Hanging:** dead hang from a bar, shoulders packed.
+
+## Execution
+
+1. Press the lower back into the floor and brace.
+2. Raise the legs to vertical without bending the knees more than slightly.
+3. Lower *slowly* — 3 seconds or more — stopping before the lower back arches
+   off the floor.
+
+## Cues
+
+- Lower back flat against the floor on lying versions, always.
+- The negative is the rep: lower slower than you lift.
+- Exhale on the way down to keep the ribs from flaring.
+
+## Common Mistakes
+
+- Lower back arching off the floor near the bottom.
+- Dropping the legs instead of lowering them.
+- Using momentum (swinging) on hanging versions.
+
+## Progression
+
+Bent-knee lying raise → straight-leg lying raise → hanging knee raise →
+hanging straight-leg raise → toes-to-bar