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

WorkoutsTests/ExerciseMotionTests.swift

@@ -131,7 +131,7 @@ struct ExerciseMotionTests {
             bundle.url(forResource: "figure-fixtures", withExtension: "json"),
             "figure-fixtures.json must be bundled as a WorkoutsTests resource (see project.yml)")
         let fixtures = try JSONDecoder().decode(FigureFixtures.self, from: Data(contentsOf: url))
-        #expect(fixtures.exercises.count == 64)
+        #expect(fixtures.exercises.count == 66)
 
         for exercise in fixtures.exercises {
             let resources = try #require(ExerciseMotionLibrary.resources(for: exercise.name),