export function hexToRgba(hex: string, alpha: number): string | null {
  const clean = hex.replace('#', '');
  if (!/^[0-9a-fA-F]{6}$/.test(clean)) return null;
  const r = parseInt(clean.substring(0, 2), 16);
  const g = parseInt(clean.substring(2, 4), 16);
  const b = parseInt(clean.substring(4, 6), 16);
  return `rgba(${r}, ${g}, ${b}, ${Math.max(0, Math.min(1, alpha))})`;
}