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

Workouts/Views/Exercises/ExerciseListView.swift

@@ -24,6 +24,15 @@ struct ExerciseListView: View {
     @State private var pendingWorkoutID: String? = nil
     @State private var resolvedWorkout: Workout? = nil
 
+    @Query(sort: \Workout.start, order: .reverse)
+    private var workouts: [Workout]
+
+    @State private var showingActivePrompt = false
+
+    private var activeWorkouts: [Workout] {
+        workouts.filter { $0.status == .inProgress || $0.status == .notStarted }
+    }
+
     var body: some View {
         Form {
             let sortedExercises = split.exercisesArray
@@ -67,7 +76,7 @@ struct ExerciseListView: View {
         .toolbar {
             ToolbarItem(placement: .primaryAction) {
                 Button("Start This Split") {
-                    startWorkout()
+                    confirmAndStart()
                 }
                 .disabled(split.exercisesArray.isEmpty)
             }
@@ -108,10 +117,53 @@ struct ExerciseListView: View {
         } message: { item in
             Text("Remove \"\(item.name)\" from this split?")
         }
+        .confirmationDialog(
+            activePromptTitle,
+            isPresented: $showingActivePrompt,
+            titleVisibility: .visible
+        ) {
+            Button("End Current & Start New") { endActiveThenStart() }
+            Button("Start in Parallel") { start() }
+            Button("Cancel", role: .cancel) { showingActivePrompt = false }
+        } message: {
+            Text(activePromptMessage)
+        }
     }
 
     // MARK: - Helpers
 
+    private var activePromptTitle: String {
+        activeWorkouts.count == 1 ? "Workout in Progress" : "\(activeWorkouts.count) Workouts in Progress"
+    }
+
+    private var activePromptMessage: String {
+        let n = activeWorkouts.count
+        let those = n == 1 ? "it" : "them"
+        return "You already have \(n == 1 ? "a workout" : "\(n) workouts") going. End \(those) first, or run this one alongside."
+    }
+
+    /// Prompt before starting if other workouts are still going; otherwise start straight away.
+    private func confirmAndStart() {
+        if activeWorkouts.isEmpty {
+            start()
+        } else {
+            showingActivePrompt = true
+        }
+    }
+
+    /// End every in-flight workout (keeping its progress), then start this split.
+    private func endActiveThenStart() {
+        let toEnd = activeWorkouts.map { WorkoutDocument(from: $0) }
+        showingActivePrompt = false
+        Task {
+            for var doc in toEnd {
+                doc.endKeepingProgress()
+                await sync.save(workout: doc)
+            }
+        }
+        start()
+    }
+
     private func pollForWorkout(id: String) {
         Task {
             // Give the file→observer→cache loop a moment to complete (typically < 1 s).
@@ -141,8 +193,8 @@ struct ExerciseListView: View {
         Task { await sync.save(split: doc) }
     }
 
-    private func startWorkout() {
-        let start = Date()
+    private func start() {
+        let startDate = Date()
         let logs = split.exercisesArray.enumerated().map { i, ex in
             WorkoutLogDocument(
                 id: ULID.make(), exerciseName: ex.name, order: i,
@@ -150,7 +202,7 @@ struct ExerciseListView: View {
                 loadType: ex.loadType, durationSeconds: ex.durationTotalSeconds,
                 currentStateIndex: 0, completed: false,
                 status: WorkoutStatus.notStarted.rawValue,
-                notes: nil, date: start
+                notes: nil, date: startDate
             )
         }
         let doc = WorkoutDocument(
@@ -158,11 +210,11 @@ struct ExerciseListView: View {
             id: ULID.make(),
             splitID: split.id,
             splitName: split.name,
-            start: start,
+            start: startDate,
             end: nil,
             status: WorkoutStatus.notStarted.rawValue,
-            createdAt: start,
-            updatedAt: start,
+            createdAt: startDate,
+            updatedAt: startDate,
             logs: logs
         )
         Task {