Keep the iPhone screen awake for the whole app session

Move the idle-timer disable out of ExerciseView/ExerciseProgressView and
up to the app scene, re-asserting it whenever the scene becomes active
(iOS clears the flag on background). A propped-up phone now stays lit for
the entire workout, not just while an exercise is open.

Claude-Session: https://claude.ai/code/session_01SCv7zvGFcKy47KSTnTLxRe

Workouts/Views/WorkoutLogs/ExerciseView.swift

@@ -10,7 +10,6 @@
 import SwiftUI
 import SwiftData
 import Charts
-import UIKit
 
 struct ExerciseView: View {
     @Environment(SyncEngine.self) private var sync
@@ -68,13 +67,10 @@ struct ExerciseView: View {
         .onAppear {
             refreshDocIfNeeded()
             progress = log?.currentStateIndex ?? 0
-            // Keep the screen lit while logging sets — a mid-workout sleep is annoying.
-            UIApplication.shared.isIdleTimerDisabled = true
             // Take over this run: the watch parks and locks it while we're editing here.
             services.watchBridge.setEditingWorkout(workout.id)
         }
         .onDisappear {
-            UIApplication.shared.isIdleTimerDisabled = false
             services.watchBridge.setEditingWorkout(nil)
         }
         // Reflect external changes (e.g. a set completed on the watch) live. Each edit