As a player, I want to choose to play on zen mode from within the game, so that I can play the way I want when I want.

Acceptance Criteria

1. Add a "Zen Mode" button in-game.
2. When a player clicks on Zen Mode, surface a modal that says "Switch to Zen Mode?" as a title, with "Turning on Zen Mode will allow you to explore freely without a timer, but you will not be able to participate in the leaderboard for this round."
3. If the player clicks to confirm on the modal in #2, the player's clock will be stopped and not counted towards the leaderboard. The player can still (if we implement these) collect a room count for rewards redemption.
4. If a player clicks to turn off Zen Mode, surface a modal that says "Switch back to Normal Mode?" as a title, with "Turning off Zen Mode will allow you to explore with a timer. You will not be able to participate in the leaderboard for this round, as the game has already begun, but your next round will start in Normal Mode."
5. If a player clicks on Zen Mode for Round 1, and completes Round 1 in Zen Mode, then Round 2 will start in Zen Mode. If the player clicked on Zen Mode for Round 1, but turns Zen Mode off before completing Round 1 (and then completes Round 1), then Round 2 will start in Normal Mode.