Make Apple Health workout recording watch-only

The phone no longer writes estimated Health workouts: the watch, which
runs the live session, is the sole recorder. Replaces WorkoutHealthWriter
with a WorkoutHealthDeleter that only removes a legacy phone-estimate
workout when its record is deleted here, drops the MET calorie table and
the phone's write/read Health scopes, and keeps phoneEstimate decodable
for existing documents.

Claude-Session: https://claude.ai/code/session_01HJDQQDA9QdP8zByg43H5v3

Workouts/HealthKit/WorkoutLauncher.swift

@@ -30,9 +30,8 @@ final class WorkoutLauncher {
 
     /// Ask watchOS to launch the Watch app into the workout. Best-effort: no-ops where
     /// HealthKit is unavailable (e.g. iPad without it) and silently tolerates a missing
-    /// or unreachable paired watch. Authorization is requested up front by
-    /// `WorkoutHealthWriter` at launch, so we only need the workout-share scope that
-    /// `startWatchApp(toHandle:)` itself requires.
+    /// or unreachable paired watch. Requests the workout-share scope that
+    /// `startWatchApp(toHandle:)` itself requires (also enough for a legacy Health delete).
     func launchWatchWorkout(activityType: HKWorkoutActivityType) {
         guard HKHealthStore.isHealthDataAvailable() else { return }
         Task {