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 Watch App/Views/ExerciseProgressView.swift

@@ -163,11 +163,11 @@ struct ExerciseProgressView: View {
     /// page-index math below depends on it.
     private var showsReady: Bool { debugInitialPage == nil && !enteredViaFlow }
 
-    /// This split runs as a continuous flow — finishing one exercise rests, then
+    /// This routine runs as a continuous flow — finishing one exercise rests, then
     /// auto-advances into the next — rather than returning to the list per exercise.
     private var autoAdvance: Bool { doc.autoAdvance == true }
 
-    /// Rest length for this run: the split's per-split override, else the global default.
+    /// Rest length for this run: the routine's per-routine override, else the global default.
     /// Governs both between-set rests and (in flow mode) the between-exercise rest.
     private var effectiveRest: Int { max(1, doc.restSeconds ?? restSeconds) }