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

README.md

@@ -24,6 +24,10 @@ your own iCloud Drive.
   page with **One More** and a **Done** that auto-completes after a countdown. A
   phase-dot row (purple work, teal rest) tracks progress. Rest time and the
   auto-finish countdown are configurable; changes sync back to the phone.
+- **Live workout mirror** — prop your iPhone up during an Apple Watch workout and it
+  mirrors the run in real time: the same Ready → work/rest → Finish flow with live
+  timers, following the watch set by set. It's read-only — the watch stays in control,
+  and the timers stay in step because each device counts off shared start times.
 - **iCloud Drive sync** — your data lives as human-readable JSON in your iCloud
   Drive, synced across devices and visible in the Files app. iCloud is required.