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.

Shared/Model/Enums.swift

@@ -35,6 +35,24 @@ enum LoadType: Int, CaseIterable, Codable, Sendable {
     }
 }
 
+/// Which segment of a split an exercise belongs to — the split screen groups its
+/// exercise list by this. Persisted as its raw `Int` value; `main` is the default
+/// (and what older documents without the field decode to).
+enum ExerciseCategory: Int, CaseIterable, Codable, Sendable {
+    case main = 0
+    case warmup = 1
+
+    /// Order the categories appear on screen: warm-up first, then the main circuit.
+    static let displayOrder: [ExerciseCategory] = [.warmup, .main]
+
+    var displayName: String {
+        switch self {
+        case .main: "Main Circuit"
+        case .warmup: "Warm-up"
+        }
+    }
+}
+
 /// The kind of training a split represents — used to tag the Apple Health workout
 /// so it lands in the right category (and credits the rings correctly), and to pick
 /// a MET value when the phone has to estimate calories without watch sensor data.