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