Mirror a live Apple Watch run on a propped-up iPhone

Add an ephemeral live-run presence channel (separate from the durable
iCloud progress sync) so a propped-up iPhone can mirror the Watch's
Ready → work/rest → Finish flow in real time as the user swipes.

Watch drives, phone mirrors (read-only), so there's no echo loop:
- Watch's ExerciseProgressView broadcasts a LiveProgress frame on every
  phase transition (and an ended signal on leave) via sendMessage,
  reachable-only — throwaway presence, never written to iCloud.
- Timers ride as wall-clock anchors (Date kept native in the WC dict to
  preserve sub-second precision), so both devices count independently
  off shared start times and stay in lockstep without streaming ticks.
- Phone holds a transient LiveRunState; ContentView auto-presents a
  read-only LiveProgressMirrorView full-screen cover while a run is live.

Claude-Session: https://claude.ai/code/session_01SCv7zvGFcKy47KSTnTLxRe

Workouts/ContentView.swift

@@ -8,7 +8,18 @@
 import SwiftUI
 
 struct ContentView: View {
+    @Environment(LiveRunState.self) private var liveRun
+
     var body: some View {
         WorkoutLogsView()
+            // Prop the phone up and it mirrors a live workout running on the Apple Watch.
+            .fullScreenCover(isPresented: Binding(
+                get: { liveRun.presentable != nil },
+                set: { presenting in if !presenting { liveRun.mute() } }
+            )) {
+                if let frame = liveRun.presentable {
+                    LiveProgressMirrorView(progress: frame) { liveRun.mute() }
+                }
+            }
     }
 }