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

Shared/Model/Enums.swift

@@ -35,9 +35,8 @@ enum LoadType: Int, CaseIterable, Codable, Sendable {
     }
 }
 
-/// The kind of training a split represents — used to tag the Apple Health workout
-/// so it lands in the right category (and credits the rings correctly), and to pick
-/// a MET value when the phone has to estimate calories without watch sensor data.
+/// The kind of training a split represents — used to tag the watch's Apple Health
+/// workout so it lands in the right category (and credits the rings correctly).
 /// Persisted as its raw `Int` on `SplitDocument`; the `HKWorkoutActivityType`
 /// mapping lives in `Shared/HealthKit/HealthKitMapping.swift` to keep this enum
 /// HealthKit-free.
@@ -70,23 +69,13 @@ enum WorkoutActivityType: Int, CaseIterable, Codable, Sendable {
         case .cycling: "figure.outdoor.cycle"
         }
     }
-
-    /// Metabolic-equivalent value used only for the phone-side calorie estimate
-    /// (`kcal ≈ MET × bodyweightKg × hours`) when no watch metrics are available.
-    var met: Double {
-        switch self {
-        case .traditionalStrength: 5.0
-        case .functionalStrength: 4.0
-        case .hiit: 8.0
-        case .coreTraining: 4.0
-        case .cardio: 7.0
-        case .cycling: 7.5
-        }
-    }
 }
 
-/// Where a workout's health metrics came from: real watch sensors, or a phone-side
-/// estimate written when no watch session ran. Persisted in `WorkoutMetrics`.
+/// Where a workout's health metrics came from: real watch sensors, or — for records
+/// written by app versions up to 2.x — a phone-side MET estimate made when no watch
+/// session ran. The phone no longer writes estimates (recording is watch-only), but
+/// `phoneEstimate` is retained so legacy documents on disk still decode. Persisted in
+/// `WorkoutMetrics`.
 enum MetricSource: String, Codable, Sendable {
     case watch
     case phoneEstimate