Add Japan map (#2106)

## Description:

This PR adds a new Japan map.

<img width="975" height="967" alt="スクリーンショット 2025-09-28 18 06 11"
src="https://github.com/user-attachments/assets/5ef06c1a-f020-4109-a5df-3cba7a9a074f"
/>

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

aotumuri

src/core/configuration/DefaultConfig.ts

@@ -63,6 +63,7 @@ const numPlayersConfig = {
   [GameMapType.Halkidiki]: [100, 50, 40],
   [GameMapType.Iceland]: [50, 40, 30],
   [GameMapType.Italia]: [50, 30, 20],
+  [GameMapType.Japan]: [20, 15, 10],
   [GameMapType.Mars]: [70, 40, 30],
   [GameMapType.Mena]: [70, 50, 40],
   [GameMapType.Montreal]: [60, 40, 30],