// Non-blocking debounce — no delay(), the loop stays responsive.
class Button {
  uint8_t pin; bool stable = HIGH, last = HIGH; unsigned long changedAt = 0;
public:
  explicit Button(uint8_t p) : pin(p) { pinMode(p, INPUT_PULLUP); }

  // Returns true once per physical press.
  bool pressed() {
    bool now = digitalRead(pin);
    if (now != last) { last = now; changedAt = millis(); }
    if (millis() - changedAt > 25 && now != stable) {
      stable = now;
      return stable == LOW;       // active-low with INPUT_PULLUP
    }
    return false;
  }
};