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/Mappers.swift

@@ -18,7 +18,8 @@ extension ExerciseDocument {
         self.init(id: e.id, name: e.name, order: e.order, sets: e.sets, reps: e.reps,
                   weight: e.weight, loadType: e.loadType, durationSeconds: e.durationTotalSeconds,
                   weightLastUpdated: e.weightLastUpdated,
-                  weightReminderWeeks: e.weightReminderTimeIntervalWeeks)
+                  weightReminderWeeks: e.weightReminderTimeIntervalWeeks,
+                  category: e.categoryRaw)
     }
 }
 
@@ -108,7 +109,8 @@ enum CacheMapper {
         Exercise(id: d.id, name: d.name, order: d.order, sets: d.sets, reps: d.reps, weight: d.weight,
                  loadType: d.loadType, durationTotalSeconds: d.durationSeconds,
                  weightLastUpdated: d.weightLastUpdated,
-                 weightReminderTimeIntervalWeeks: d.weightReminderWeeks)
+                 weightReminderTimeIntervalWeeks: d.weightReminderWeeks,
+                 categoryRaw: d.category ?? ExerciseCategory.main.rawValue)
     }
 
     private static func apply(_ d: ExerciseDocument, to e: Exercise) {
@@ -121,6 +123,7 @@ enum CacheMapper {
         e.durationTotalSeconds = d.durationSeconds
         e.weightLastUpdated = d.weightLastUpdated
         e.weightReminderTimeIntervalWeeks = d.weightReminderWeeks
+        e.categoryRaw = d.category ?? ExerciseCategory.main.rawValue
     }
 
     // MARK: Workout