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/Hollow Body Hold/frames/frame-1.svg

@@ -0,0 +1,16 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 180" fill="none">
+  <title>Hollow Body Hold</title>
+  <line x1="16" y1="156" x2="304" y2="156" stroke="#b9bec9" stroke-width="3" stroke-linecap="round"/>
+  <path id="leg_l" d="M 191.0 150.0 L 237.0 150.0 L 277.0 150.0" stroke="#a9afba" stroke-width="5" stroke-linecap="round" stroke-linejoin="round"/>
+  <path id="spine" d="M 185.0 148.0 Q 141.5 148.0 100.0 148.0" stroke="#0d9488" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path id="arm_r" d="M 100.0 148.0 L 70.0 148.0 L 40.0 148.0" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path id="leg_r" d="M 185.0 148.0 L 231.0 148.0 L 271.0 148.0" stroke="#3a3f4b" stroke-width="6" stroke-linecap="round" stroke-linejoin="round"/>
+  <circle id="head" cx="80.4" cy="143.8" r="10" fill="white" stroke="#3a3f4b" stroke-width="6"/>
+  <line id="nose" x1="80.4" y1="133.8" x2="80.4" y2="126.8" stroke="#3a3f4b" stroke-width="4" stroke-linecap="round"/>
+  <g font-family="-apple-system, Helvetica, sans-serif" font-size="11" fill="#6b7180">
+    <line x1="242" y1="16" x2="258" y2="16" stroke="#3a3f4b" stroke-width="4" stroke-linecap="round"/>
+    <text x="264" y="20">R</text>
+    <line x1="282" y1="16" x2="298" y2="16" stroke="#a9afba" stroke-width="4" stroke-linecap="round"/>
+    <text x="304" y="20">L</text>
+  </g>
+</svg>