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.

Shared/Model/Entities.swift

@@ -24,6 +24,8 @@ final class Split {
     var updatedAt: Date = Date()
     var jsonRelativePath: String = ""
     var activityTypeRaw: Int = 0
+    var restSeconds: Int?
+    var autoAdvance: Bool?
 
     @Relationship(deleteRule: .cascade, inverse: \Exercise.split)
     var exercises: [Exercise] = []
@@ -148,6 +150,8 @@ final class Workout {
     /// phone re-derives them into any `WorkoutDocument` it rebuilds and the merge stays
     /// deletion-safe across cache round-trips. Phone-authored; see `WorkoutMergePlanner`.
     var deletedLogIDs: [String: Date]?
+    var restSeconds: Int?
+    var autoAdvance: Bool?
 
     @Relationship(deleteRule: .cascade, inverse: \WorkoutLog.workout)
     var logs: [WorkoutLog] = []