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/Splits/SplitAddEditView.swift

@@ -29,6 +29,9 @@ struct SplitAddEditView: View {
     @State private var color: String = "indigo"
     @State private var systemImage: String = "dumbbell.fill"
     @State private var activityType: WorkoutActivityType = .traditionalStrength
+    @State private var autoAdvance: Bool = false
+    @State private var restOverrideEnabled: Bool = false
+    @State private var restSecondsValue: Int = 45
     @State private var showingIconPicker: Bool = false
     @State private var showingDeleteConfirmation: Bool = false
 
@@ -42,6 +45,9 @@ struct SplitAddEditView: View {
             _color = State(initialValue: split.color)
             _systemImage = State(initialValue: split.systemImage)
             _activityType = State(initialValue: split.activityTypeEnum)
+            _autoAdvance = State(initialValue: split.autoAdvance ?? false)
+            _restOverrideEnabled = State(initialValue: split.restSeconds != nil)
+            _restSecondsValue = State(initialValue: split.restSeconds ?? 45)
         }
     }
 
@@ -111,6 +117,25 @@ struct SplitAddEditView: View {
                 Text("Determines how this workout is categorized in Apple Health and how it credits your Activity rings.")
             }
 
+            Section {
+                Toggle("Auto-Advance Exercises", isOn: $autoAdvance)
+
+                Toggle("Custom Rest Time", isOn: $restOverrideEnabled)
+                if restOverrideEnabled {
+                    Stepper(value: $restSecondsValue, in: 10...180, step: 5) {
+                        HStack {
+                            Text("Rest Time")
+                            Spacer()
+                            Text("\(restSecondsValue)s").foregroundColor(.secondary)
+                        }
+                    }
+                }
+            } header: {
+                Text("Rest & Pacing")
+            } footer: {
+                Text("Auto-Advance flows from one exercise to the next with a rest between, so you can run the whole split hands-free. Custom Rest Time sets this split's rest — used between sets, and between exercises when auto-advancing; otherwise the Settings default applies.")
+            }
+
             if let split = split {
                 Section(header: Text("Exercises")) {
                     NavigationLink {
@@ -178,6 +203,8 @@ struct SplitAddEditView: View {
             doc.color = color
             doc.systemImage = systemImage
             doc.activityType = activityType.rawValue
+            doc.restSeconds = restOverrideEnabled ? restSecondsValue : nil
+            doc.autoAdvance = autoAdvance ? true : nil
             doc.updatedAt = Date()
             Task { await sync.save(split: doc) }
         } else {
@@ -193,7 +220,9 @@ struct SplitAddEditView: View {
                 createdAt: Date(),
                 updatedAt: Date(),
                 exercises: [],
-                activityType: activityType.rawValue
+                activityType: activityType.rawValue,
+                restSeconds: restOverrideEnabled ? restSecondsValue : nil,
+                autoAdvance: autoAdvance ? true : nil
             )
             Task { await sync.save(split: doc) }
         }