End the watch session on Discard, plus start-flow UX tweaks

Watch-side follow-through for the End Workout flow:
- The phone now pushes an authoritative set (in-progress, not-started, and
  completed within 24h) instead of the 25 most-recent workouts, and the watch
  prunes any workout absent from it. So a Discard/Delete (or a completed run aging
  out) drops off the watch, empties its active list, and ends the HKWorkoutSession
  — fixing the persistent wrist-raise re-foregrounding. The watch never originates
  a workout, so pruning can't lose local data; the 24h grace keeps a just-finished
  run on screen. The gate pops if the run you're viewing is pruned.

UX tweaks:
- The in-workout ⋯ is now a pull-down Menu (Add Exercise / End Workout) rather than
  an action sheet.
- Starting a split while another workout is still active now prompts to end the
  current one(s) — keeping their progress — or run in parallel. Wired into both
  start paths (the split picker and "Start This Split"), via a shared
  WorkoutDocument.endKeepingProgress() helper.

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

CHANGELOG.md

@@ -1,5 +1,9 @@
 **June 2026**
 
+Starting a new workout while another is still going now asks whether to end the current one first or run both in parallel.
+
+Discarding or deleting an in-progress workout on iPhone now takes your Apple Watch out of the workout too, so the watch no longer keeps waking to the workout app when you raise your wrist.
+
 You can now end a workout before finishing every exercise: open the ⋯ menu and choose End Workout, then Save to keep what you did — any exercises you didn't get to are marked skipped — or Discard to remove the workout.
 
 Right after you turn on iCloud Drive, Workouts now waits for it to finish coming online instead of giving up and showing the "turn on iCloud Drive" screen too soon. The connecting screen also keeps you posted as it works, letting you know the first connect can take a moment.