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/WorkoutLogs/ExerciseProgressView.swift

@@ -30,6 +30,10 @@ struct ExerciseProgressView: View {
     @Environment(\.dismiss) private var dismiss
     @Environment(\.verticalSizeClass) private var verticalSizeClass
 
+    /// Live watch-forwarded heart rate (see `LiveRunState.heartRate`) — drives the
+    /// target-HR pill when this run carries a `targetHeartRate`.
+    @Environment(LiveRunState.self) private var liveRun
+
 
     /// The shared working workout document owned by the parent list. We mutate the
     /// matching log in place and ask the parent to persist each change — driving the UI
@@ -391,6 +395,9 @@ struct ExerciseProgressView: View {
                         .padding(.bottom, 8)
                 }
             }
+            .overlay(alignment: .top) {
+                heartRatePill
+            }
 
             // Bottom half: the looping form-guide figure. Shows the *next* exercise while
             // resting between exercises (a live preview of what's coming up), otherwise this
@@ -731,6 +738,33 @@ struct ExerciseProgressView: View {
         }
     }
 
+    // MARK: - Live heart rate vs. target
+
+    /// Live heart rate against this run's target (cardio routines only): the bpm the
+    /// watch is streaming, tinted by band, with a cue to ease off (arrow down) or push
+    /// harder (arrow up) — how you dial in a treadmill incline from a propped phone.
+    /// Renders nothing unless the run carries a target *and* a fresh sample exists, so
+    /// it has zero footprint on strength runs or when the watch isn't active.
+    @ViewBuilder
+    private var heartRatePill: some View {
+        if let target = doc.targetHeartRate, let bpm = liveRun.heartRate {
+            let band = HeartRateBand(bpm: bpm, target: target)
+            HStack(spacing: 6) {
+                Image(systemName: "heart.fill")
+                Text("\(Int(bpm.rounded()))")
+                    .monospacedDigit()
+                Image(systemName: band.cueSymbol)
+            }
+            .font(.subheadline.weight(.semibold))
+            .foregroundStyle(band.tint)
+            .padding(.horizontal, 14)
+            .padding(.vertical, 7)
+            .background(.quaternary.opacity(0.5), in: Capsule())
+            .padding(.top, 6)
+            .animation(.easeInOut(duration: 0.3), value: band)
+        }
+    }
+
     // MARK: - Adjust the last set's entry
 
     /// The just-completed set's recorded entry, shown on the rest and finish pages
@@ -1119,6 +1153,27 @@ private enum WorkoutHaptic {
     }
 }
 
+// MARK: - Heart-rate band presentation
+
+private extension HeartRateBand {
+    /// The correction cue: below target → push harder (up), above → ease off (down).
+    var cueSymbol: String {
+        switch self {
+        case .low: "arrow.up"
+        case .inRange: "checkmark"
+        case .high: "arrow.down"
+        }
+    }
+
+    var tint: Color {
+        switch self {
+        case .low: .blue
+        case .inRange: .green
+        case .high: .orange
+        }
+    }
+}
+
 // MARK: - Phase Colors
 
 private extension Color {