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/WorkoutMergePlannerTests.swift

@@ -26,8 +26,8 @@ struct WorkoutMergePlannerTests {
                          logs: [WorkoutLogDocument], deletedLogIDs: [String: Date]? = nil,
                          metrics: WorkoutMetrics? = nil, end: Date? = nil) -> WorkoutDocument {
         WorkoutDocument(
-            schemaVersion: WorkoutDocument.currentSchemaVersion, id: "W", splitID: nil,
-            splitName: nil, start: Self.t0, end: end, status: status.rawValue,
+            schemaVersion: WorkoutDocument.currentSchemaVersion, id: "W", routineID: nil,
+            routineName: nil, start: Self.t0, end: end, status: status.rawValue,
             createdAt: Self.t0, updatedAt: updatedAt, logs: logs, metrics: metrics,
             deletedLogIDs: deletedLogIDs)
     }