Add "Four Islands" 🏝️ to the playlist (Based on feedback) (#2679)

## Description:

Saw a few people in the OF Discord missing that map in the playlist.
As far as I know, it wasn’t added because Evan was worried about
stalemates.
But since the map is fairly small (1500x1500) and two hydros can destroy
an entire island, it shouldn’t be any more prone to stalemates than
Baikal (2500x1500).
Could deliver some variety (Nuke-heavy gameplay). And especially crazy
team games.

<img width="332" height="52" alt="Screenshot 2025-12-23 011703"
src="https://github.com/user-attachments/assets/c4e60d83-6af3-4515-9d19-8dbfac380506"
/>
<img width="552" height="406" alt="Screenshot 2025-12-23 021755"
src="https://github.com/user-attachments/assets/6941fcf6-cdd2-41e1-a1de-d55739f626f8"
/>
<img width="528" height="73" alt="Screenshot 2025-12-23 014455"
src="https://github.com/user-attachments/assets/d90a77e7-cc66-4137-9d05-913120d71ac5"
/>
<img width="530" height="79" alt="Screenshot 2025-12-23 014421"
src="https://github.com/user-attachments/assets/2903ad57-9eaa-480e-80ed-4dcb6c695c60"
/>
<img width="543" height="336" alt="Screenshot 2025-12-23 021657"
src="https://github.com/user-attachments/assets/e84497bf-4fb8-44a3-be59-8208fd9a7312"
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<img width="531" height="80" alt="Screenshot 2025-12-23 014355"
src="https://github.com/user-attachments/assets/974a6843-a262-473b-ba51-c795c0e42eae"
/>
<img width="528" height="402" alt="Screenshot 2025-12-23 012506"
src="https://github.com/user-attachments/assets/fa182e7e-3a72-4217-b65c-92fc84e4e4e7"
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<img width="458" height="100" alt="Screenshot 2025-12-23 011954"
src="https://github.com/user-attachments/assets/4edb499a-86d8-43f1-aa58-f1e72a87f179"
/>
<img width="424" height="123" alt="Screenshot 2025-12-23 011920"
src="https://github.com/user-attachments/assets/099851b3-129e-484e-a7d0-befafcee918d"
/>
<img width="536" height="125" alt="Screenshot 2025-12-23 011829"
src="https://github.com/user-attachments/assets/118d956b-bec4-48f6-9a6d-abf699170774"
/>
<img width="419" height="67" alt="Screenshot 2025-12-23 021732"
src="https://github.com/user-attachments/assets/27b9536e-1a71-463a-a506-93174508dc2b"
/>

## 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:

FloPinguin

src/server/MapPlaylist.ts

@@ -36,6 +36,7 @@ const frequency: Partial<Record<GameMapName, number>> = {
   EuropeClassic: 3,
   FalklandIslands: 4,
   FaroeIslands: 4,
+  FourIslands: 4,
   GatewayToTheAtlantic: 5,
   GulfOfStLawrence: 4,
   Halkidiki: 4,