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.

CHANGELOG.md

@@ -1,5 +1,11 @@
 **July 2026**
 
+A new Auto-Advance option lets a split flow hands-free from one exercise to the next, resting automatically between them.
+
+Each split can now set its own rest time, overriding the app-wide default in Settings.
+
+The Morning Wake-Up starter split is now a timed routine that auto-advances through every move.
+
 Tap the speaker on any library exercise to hear its full instructions read aloud.
 
 Turn on Speak Exercise Cues in Settings to hear each exercise's setup and form cues spoken automatically when you start it, hands-free.