Add per-split rest length and hands-free auto-advance flow

Two per-split settings, with the global Settings values as defaults:

- restSeconds: Int? — per-split rest, used between sets and (in flow) between
  exercises; nil falls back to the global default.
- autoAdvance: Bool? — flow mode: finishing an exercise rests, then opens the
  next one hands-free, all the way through the split.

Both are optional, snapshotted onto WorkoutDocument at the start sites (no live
split link), and not schema-bumped — same degradation pattern as activityType.

A thin RunFlowView wrapper (iOS + watch) owns the on-screen log and swaps it via
.id(currentLogID) on hand-off, so the per-exercise ExerciseProgressView stays
per-logID and untouched; the between-exercise rest reuses the existing .rest
countdown as the terminal page. The mirror reuses the per-logID live channel:
the wrapper suppresses the boundary .ended teardown so it follows across
exercises, and ContentView re-keys the cover on frame.logID — no sync-bridge
changes.

Morning Wake-Up ships as a flowing 45s-work / 15s-rest routine.

New Rest & Pacing section in the split editor exposes both controls.

Workouts/Views/WorkoutLogs/WorkoutLogsView.swift

@@ -297,7 +297,8 @@ struct SplitPickerSheet: View {
             status: WorkoutStatus.notStarted.rawValue,
             createdAt: startDate,
             updatedAt: startDate,
-            logs: logs
+            logs: logs,
+            restSeconds: split.restSeconds, autoAdvance: split.autoAdvance
         )
 
         // Hand the id back after the save so the presenter can poll the cache and