Enable only one newly created marker on the map

[tzuyi126]

https://github.com/user-attachments/assets/dfba58d8-43fb-4314-a1db-1523a3f5c426

• Only one newly created marker can be displayed on the map.
• If user clicks on other location on the map, the previous marker disappears.
• If user uploads a sound file to that location, the marker stays.

I also did some refactor to the map.js, removing duplicate codes for adding marker on the map.