Add per-routine target heart rate with live in-run indicator

Endurance routines (HIIT, cardio, cycling) can carry an optional target bpm
(RoutineDocument.targetHeartRate, not schema-bumped — same preference-field
rationale as restSeconds/autoAdvance), snapshotted onto the WorkoutDocument at
plan time like the other pacing fields.

During a run, the watch streams its live HR sample to the phone over a new
best-effort liveHeartRate message — deliberately outside the LiveProgress
machinery (no version bump, no staging/retry; a gauge, not a record), throttled
to changed-bpm-or-10s in the watch bridge. LiveRunState holds the sample with a
30s staleness auto-clear so a dead stream never shows a frozen number.

Both run screens show the reading only when the run carries a target: the
phone's ExerciseProgressView as a top pill, the watch's in the top-trailing
toolbar slot, each tinted by a shared ±5 bpm HeartRateBand with an arrow cue to
push harder (low) or ease off (high) — e.g. dialing in a treadmill incline to
hold a steady effort.

Claude-Session: https://claude.ai/code/session_01Y7ZhkCYWNiTSAFhFCGnJ8n

Workouts/Views/Routines/RoutineAddEditView.swift

@@ -32,6 +32,8 @@ struct RoutineAddEditView: View {
     @State private var autoAdvance: Bool = false
     @State private var restOverrideEnabled: Bool = false
     @State private var restSecondsValue: Int = 45
+    @State private var targetHREnabled: Bool = false
+    @State private var targetHRValue: Int = 135
     @State private var showingIconPicker: Bool = false
     @State private var showingDeleteConfirmation: Bool = false
 
@@ -48,6 +50,8 @@ struct RoutineAddEditView: View {
             _autoAdvance = State(initialValue: routine.autoAdvance ?? false)
             _restOverrideEnabled = State(initialValue: routine.restSeconds != nil)
             _restSecondsValue = State(initialValue: routine.restSeconds ?? 45)
+            _targetHREnabled = State(initialValue: routine.targetHeartRate != nil)
+            _targetHRValue = State(initialValue: routine.targetHeartRate ?? 135)
         }
     }
 
@@ -136,6 +140,26 @@ struct RoutineAddEditView: View {
                 Text("Auto-Advance flows from one exercise to the next with a rest between, so you can run the whole routine hands-free. Custom Rest Time sets this routine's rest — used between sets, and between exercises when auto-advancing; otherwise the Settings default applies.")
             }
 
+            // Only endurance types get a target — a strength set's HR swings by design.
+            if activityType.supportsHeartRateTarget {
+                Section {
+                    Toggle("Target Heart Rate", isOn: $targetHREnabled)
+                    if targetHREnabled {
+                        Stepper(value: $targetHRValue, in: 80...200, step: 5) {
+                            HStack {
+                                Text("Target")
+                                Spacer()
+                                Text("\(targetHRValue) bpm").foregroundColor(.secondary)
+                            }
+                        }
+                    }
+                } header: {
+                    Text("Heart Rate")
+                } footer: {
+                    Text("During a run, the exercise screen shows your live heart rate from the watch with a cue to ease off or push harder — useful for holding a steady effort, like dialing in a treadmill incline.")
+                }
+            }
+
             if let routine = routine {
                 Section(header: Text("Exercises")) {
                     NavigationLink {
@@ -205,6 +229,9 @@ struct RoutineAddEditView: View {
             doc.activityType = activityType.rawValue
             doc.restSeconds = restOverrideEnabled ? restSecondsValue : nil
             doc.autoAdvance = autoAdvance ? true : nil
+            // Cleared when the type no longer supports a target (the section hides).
+            doc.targetHeartRate = activityType.supportsHeartRateTarget && targetHREnabled
+                ? targetHRValue : nil
             doc.updatedAt = Date()
             Task { await sync.save(routine: doc) }
         } else {
@@ -222,7 +249,9 @@ struct RoutineAddEditView: View {
                 exercises: [],
                 activityType: activityType.rawValue,
                 restSeconds: restOverrideEnabled ? restSecondsValue : nil,
-                autoAdvance: autoAdvance ? true : nil
+                autoAdvance: autoAdvance ? true : nil,
+                targetHeartRate: activityType.supportsHeartRateTarget && targetHREnabled
+                    ? targetHRValue : nil
             )
             Task { await sync.save(routine: doc) }
         }