Save workouts to Apple Health with live watch metrics and a post-workout summary

Watch sessions now run an HKLiveWorkoutBuilder: heart rate and active
energy are collected live (shown in an in-workout HUD), saved to Health
as a real HKWorkout on completion, and carried back to the phone as
WorkoutMetrics on the workout document. Phone-only workouts get an
estimated Health workout (MET x bodyweight x duration) after a 10s
debounce that a late-arriving watch session cancels; a launch sweep
backfills workouts completed within the last day. Dedupe is keyed on
metrics.healthKitWorkoutUUID plus the metrics source.

Splits gain an activity type (strength, functional, HIIT, core, cardio,
cycling) that categorizes the Health workout and picks the MET value.
A post-workout summary sheet (duration, calories, avg/max HR, HR zones,
total volume) fills in live and is also shown on completed workouts.
Weights can now display in lb or kg (display-only relabel), synced to
the watch over the existing application context.

WorkoutDocument schema 1->2 (metrics are irreplaceable, so older apps
must quarantine rather than strip them); cache schema 2 rebuilds the
SwiftData store with the new metric columns. Deleting a workout in the
app intentionally leaves its Health record in place.

Shared/Model/Entities.swift

@@ -22,6 +22,7 @@ final class Split {
     var createdAt: Date = Date()
     var updatedAt: Date = Date()
     var jsonRelativePath: String = ""
+    var activityTypeRaw: Int = 0
 
     @Relationship(deleteRule: .cascade, inverse: \Exercise.split)
     var exercises: [Exercise] = []
@@ -41,6 +42,11 @@ final class Split {
     static let unnamed = "Unnamed Split"
 
     var exercisesArray: [Exercise] { exercises.sorted { $0.order < $1.order } }
+
+    var activityTypeEnum: WorkoutActivityType {
+        get { WorkoutActivityType(rawValue: activityTypeRaw) ?? .traditionalStrength }
+        set { activityTypeRaw = newValue.rawValue }
+    }
 }
 
 // MARK: - Exercise
@@ -107,6 +113,19 @@ final class Workout {
     var updatedAt: Date = Date()
     var jsonRelativePath: String = ""
 
+    // Health metrics — flat columns mirroring `WorkoutMetrics` (SwiftData @Model
+    // can't store the nested Codable cleanly). Assemble via the `metrics` computed
+    // property. All nil until a workout finishes and a writer fills them in.
+    var metricActiveEnergyKcal: Double?
+    var metricAvgHeartRate: Double?
+    var metricMaxHeartRate: Double?
+    var metricMinHeartRate: Double?
+    var metricTotalVolume: Double?
+    var metricHRZoneSeconds: [Double]?
+    var metricHealthKitWorkoutUUID: String?
+    var metricSourceRaw: String?
+    var metricRecordedAt: Date?
+
     @Relationship(deleteRule: .cascade, inverse: \WorkoutLog.workout)
     var logs: [WorkoutLog] = []
 
@@ -143,6 +162,38 @@ final class Workout {
             return start.formattedDate()
         }
     }
+
+    /// Assembles the flat `metric*` columns into a `WorkoutMetrics`, or nil when none
+    /// have been recorded. `source`/`recordedAt` are always set together when metrics
+    /// exist, so they gate presence.
+    var metrics: WorkoutMetrics? {
+        get {
+            guard let sourceRaw = metricSourceRaw,
+                  let source = MetricSource(rawValue: sourceRaw),
+                  let recordedAt = metricRecordedAt else { return nil }
+            return WorkoutMetrics(
+                activeEnergyKcal: metricActiveEnergyKcal,
+                avgHeartRate: metricAvgHeartRate,
+                maxHeartRate: metricMaxHeartRate,
+                minHeartRate: metricMinHeartRate,
+                totalVolume: metricTotalVolume,
+                hrZoneSeconds: metricHRZoneSeconds,
+                healthKitWorkoutUUID: metricHealthKitWorkoutUUID,
+                source: source,
+                recordedAt: recordedAt)
+        }
+        set {
+            metricActiveEnergyKcal = newValue?.activeEnergyKcal
+            metricAvgHeartRate = newValue?.avgHeartRate
+            metricMaxHeartRate = newValue?.maxHeartRate
+            metricMinHeartRate = newValue?.minHeartRate
+            metricTotalVolume = newValue?.totalVolume
+            metricHRZoneSeconds = newValue?.hrZoneSeconds
+            metricHealthKitWorkoutUUID = newValue?.healthKitWorkoutUUID
+            metricSourceRaw = newValue?.source.rawValue
+            metricRecordedAt = newValue?.recordedAt
+        }
+    }
 }
 
 // MARK: - WorkoutLog