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

Scripts/generate_starter_splits.swift

@@ -183,6 +183,11 @@ let seeds: [Sp] = [
     Sp(name: "Cardio", color: "red", icon: "figure.run", activity: 4, ex: [
         Ex(name: "Cardio", sets: 1, reps: 0, load: 2, dur: 1200),
     ]),
+    // A single timed sit in a `.mindAndBody` (→ HealthKit `.mindAndBody`) split,
+    // same one-block shape as Cardio.
+    Sp(name: "Meditation", color: "purple", icon: "figure.mind.and.body", activity: 8, ex: [
+        Ex(name: "Meditation", sets: 1, reps: 0, load: 2, dur: 300),
+    ]),
 ]
 
 // MARK: - Emit