Add rest timer with toggle — auto-starts after each set when enabled

Floating banner shows circular progress + MM:SS countdown with skip button.
Haptic + system sound fires when timer reaches zero. Duration and on/off
toggle live in Settings → Rest Timer sheet.

Co-Authored-By: Kutesir <tqwyy79vzn@privaterelay.appleid.com>

KisaniCal/Models/ExerciseModels.swift

@@ -178,6 +178,9 @@ class WorkoutViewModel: ObservableObject {
     @Published var activeSections: [WorkoutSection]
     @Published var workoutDates: [String] = []
     @Published var restTimerSeconds: Int = 60
+    @Published var restTimerEnabled: Bool = false
+    @Published var restCountdown: Int = 0
+    @Published var restTimerTotal: Int = 0
     @Published var sessionStartDate: Date? = nil
 
     var streakDays: Int {
@@ -404,12 +407,14 @@ class WorkoutViewModel: ObservableObject {
               let ei = activeSections[si].exercises.firstIndex(where: { $0.id == exerciseId }),
               let setIdx = activeSections[si].exercises[ei].sets.firstIndex(where: { $0.id == setId })
         else { return }
+        let wasMarkedDone = !activeSections[si].exercises[ei].sets[setIdx].isDone
         activeSections[si].exercises[ei].sets[setIdx].isDone.toggle()
         if sessionStartDate == nil, activeSections[si].exercises[ei].sets[setIdx].isDone {
             sessionStartDate = Date()
         }
         syncBack()
         if doneSets == totalSets && totalSets > 0 { logWorkoutCompleted() }
+        if wasMarkedDone && restTimerEnabled { startRestTimer() }
     }
 
     func addSet(sectionId: UUID, to exerciseId: UUID) {
@@ -495,6 +500,18 @@ class WorkoutViewModel: ObservableObject {
         syncBack()
     }
 
+    // MARK: - Rest Timer
+
+    func startRestTimer() {
+        restTimerTotal = restTimerSeconds
+        restCountdown  = restTimerSeconds
+    }
+
+    func stopRestTimer() {
+        restCountdown = 0
+        restTimerTotal = 0
+    }
+
     private func syncBack() {
         guard let idx = programs.firstIndex(where: { $0.id == activeProgramId }) else { return }
         programs[idx].sections = activeSections