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/Screenshots/ScreenshotRootView.swift

@@ -26,7 +26,17 @@ struct ScreenshotRootView: View {
 
     @ViewBuilder
     private var content: some View {
-        if let workout = activeWorkout {
+        // The full tab shell and the Progress tab need no particular workout,
+        // so they're handled before the active-workout unwrap.
+        if ScreenshotSeed.screen(default: "workouts") == "today" {
+            ContentView()
+        } else if ScreenshotSeed.screen(default: "workouts") == "progress" {
+            ProgressTabView()
+        } else if ScreenshotSeed.screen(default: "workouts") == "progress-bottom" {
+            ProgressTabView(initialAnchor: .bottom)
+        } else if ScreenshotSeed.screen(default: "workouts") == "exercise-trends" {
+            NavigationStack { ExerciseTrendsListView() }
+        } else if let workout = activeWorkout {
             switch ScreenshotSeed.screen(default: "workouts") {
             case "exercise":
                 let logID = WorkoutDocument(from: workout).logs.first { $0.exerciseName == "Seated Row" }?.id