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/WorkoutPathBucketingTests.swift

@@ -51,8 +51,8 @@ struct WorkoutPathBucketingTests {
     /// document's own bucket is exactly what the engine writes it to.
     @Test func instancePropertyMatchesStatic() {
         let doc = WorkoutDocument(
-            schemaVersion: WorkoutDocument.currentSchemaVersion, id: "01WK", splitID: nil,
-            splitName: nil, start: date(year: 2024, month: 7), end: nil,
+            schemaVersion: WorkoutDocument.currentSchemaVersion, id: "01WK", routineID: nil,
+            routineName: nil, start: date(year: 2024, month: 7), end: nil,
             status: WorkoutStatus.notStarted.rawValue, createdAt: date(year: 2024, month: 7),
             updatedAt: date(year: 2024, month: 7), logs: [], metrics: nil
         )