Restructure into a three-tab app with Progress, goals, and Meditation

The UX redesign's first landing (spec in UX-REDESIGN.md): ContentView
becomes a Today / Progress / Settings TabView, "Routine" replaces
"Split" in every user-facing string and view name (code-level types
keep their names), and workout starting moves to shared
WorkoutStarter / StartedWorkoutNavigator plumbing.

- New Progress tab: weekly goal streaks, workout trends, per-exercise
  weight progression, achievements, and the full history list
  (WorkoutLogsView -> WorkoutHistoryView).
- Goals: stable categories workouts roll up to, managed from Settings.
- New Meditation exercise + starter routine; timed sits record to
  Apple Health as Mind & Body sessions.

Claude-Session: https://claude.ai/code/session_012qw2itfzKyEJ1HpsFt8Ex4

Workouts/Views/WorkoutLogs/ExerciseView.swift

@@ -186,7 +186,7 @@ struct ExerciseView: View {
 
     /// Apply edited machine settings: update the log's plan-time snapshot (persisted
     /// with the workout), then write the same settings back to the originating
-    /// split's exercise as the durable default — same sequencing as the workout
+    /// routine's exercise as the durable default — same sequencing as the workout
     /// list's machine sheet.
     private func applyMachineSettings(_ settings: [MachineSetting]) {
         guard let i = doc.logs.firstIndex(where: { $0.id == logID }) else { return }
@@ -195,10 +195,10 @@ struct ExerciseView: View {
         doc.updatedAt = Date()
         let snapshot = doc
         let exerciseName = doc.logs[i].exerciseName
-        let splitID = doc.splitID
+        let routineID = doc.routineID
         Task {
             await sync.save(workout: snapshot)
-            await sync.writeBackMachineSettings(settings, exerciseName: exerciseName, splitID: splitID)
+            await sync.writeBackMachineSettings(settings, exerciseName: exerciseName, routineID: routineID)
         }
     }