Timers TIMERS: - Use TimelineView(.animation) for smooth countdown/stopwatch UI - Timer.publish(every:on:in:).autoconnect() for periodic updates - @State private var timeRemaining: TimeInterval for countdown state - .onReceive(timer) { in } to update state each tick - Format with Duration.formatted() or custom mm:ss formatter - Invalidate timer in .onDisappear to prevent leaks ---