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/ExerciseProgressView.swift

@@ -181,8 +181,6 @@ struct ExerciseProgressView: View {
             }
         }
         .onAppear {
-            // Keep the screen lit while logging — a mid-workout sleep is annoying.
-            UIApplication.shared.isIdleTimerDisabled = true
             guard !didRestorePage else { return }
             if startsResumed {
                 // Resume on the first unfinished set. A paged TabView can settle on page 0
@@ -199,9 +197,6 @@ struct ExerciseProgressView: View {
                 didRestorePage = true
             }
         }
-        .onDisappear {
-            UIApplication.shared.isIdleTimerDisabled = false
-        }
     }
 
     /// Move to the resume page without animation, only if we're not already there