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/Sync/WorkoutMergePlanner.swift

@@ -64,7 +64,7 @@ enum WorkoutMergePlanner {
         // 4. Prune tombstones past the grace period.
         tombstones = tombstones.filter { now.timeIntervalSince($0.value) < tombstoneGrace }
 
-        // 5. Base scalars (splitID/name, start, metrics, …) on the newer document overall — it
+        // 5. Base scalars (routineID/name, start, metrics, …) on the newer document overall — it
         //    carries a just-attached metrics summary or a rename — then override the reconciled
         //    parts. Ties prefer the cached copy (the phone is the sole writer). Sort is
         //    id-tie-broken so the result is deterministic even when two logs share an `order`.