Make the live-run mirror survive lost phone-to-watch frames

Live frames ride sendMessage, which is reachable-only — and phone→watch
reachability drops exactly when the user is swiping on the phone (wrist
down). A frame that failed to send was staged but never retried until a
reachability edge, and a frame lost outright desynced the run until the
next human transition — sometimes forever, since a reconnect could even
re-send the stale staged frame and yank the peer backwards.

Four fixes, symmetric on both bridges and both run screens:

- A send that fails while nominally reachable now retries with a short
  backoff (a few times per staged message) instead of being swallowed.
- Receiving a frame that outranks the staged outbound one drops the
  staged frame, so a reconnect re-send can't move the run backwards;
  a delivery the staged frame outranks is ignored as stale.
- Every staleness comparison now tie-breaks the shared version sequence
  on the frame's wall-clock anchor (LiveProgress.isNewer) — after a
  lost frame both devices can mint the same version, and the later
  human action must win.
- Durable repair: when the absorbed workout doc shows sets completed
  beyond anything the open run screen recorded or followed, it jumps
  forward to the first unfinished set's work page — a lost frame now
  degrades to a briefly-stale page instead of a stuck one.

CHANGELOG.md

@@ -1,5 +1,7 @@
 **July 2026**
 
+Swiping through sets on the iPhone now reliably moves the watch along too, instead of the two drifting apart mid-workout.
+
 On Apple Watch, the workout screen now gives its whole display to the set and rest timer, without the form-guide figure shown on iPhone.
 
 Barbells and pull-up bars in the animated form guide now turn with the figure as the view circles, instead of hovering fixed on screen.