Function getNextDay

src/utils/stats.ts:847–851

* Get the next day after a given date string (YYYY-MM-DD format).

(dateStr: string)

 * Get the next day after a given date string (YYYY-MM-DD format).
 */
function getNextDay(dateStr: string): string {
  const date = new Date(dateStr)
  date.setDate(date.getDate() + 1)
  return toDateString(date)
}

function calculateStreaks(dailyActivity: DailyActivity[]): StreakInfo {
  if (dailyActivity.length === 0) {