A gaming company is launching a new mobile title expected to reach millions of concurrent players globally. The backend must record a continuous stream of player score updates and serve near-real-time leaderboard rankings. Write volume is extremely spiky and unpredictable, spiking 20x during tournaments. The team wants a fully managed data store that scales writes seamlessly without capacity planning, delivers single-digit millisecond latency, and minimizes operational overhead. Sorted top-N leaderboard reads must remain fast even at peak. Which design best meets these requirements?