Hotfix #3

Changes :
- Increased overall sound volume.
- Fixed an issue where the selected language would not be retained after restarting the game.
- The "Game Saved" UI now appears at save points.
- Added small whirlwinds in the early upstream section for smoother gameplay.
- Reduced the flow speed in the late upstream section by approximately 8%.
(We found that excessive flow speed was affecting some players depending on their play environment. We adjusted the related coefficients to prevent this from impacting the game difficulty for those players.)