Adds map "The Straits" (#3896)

## Description:

**Adds "The Straits" map:**

A map located around Denmark and the many surrounding straits: Kattegat,
Skagerrak and the Danish straits (thus the name, meant to be a creative
name like "Between Two Seas" and "Gateway to the Atlantic"). This map is
themed in the early 1900s, the nations/NPCs are traditional and
historical regions of Sweden-Norway, Denmark and the Germany.

Relatively small map with ~700k land tiles, similar to World

Inspired by this Discord thread with nearly 20 upvotes:
https://canary.discord.com/channels/1284581928254701718/1482089104110911634/1482089104110911634

<img width="365" height="506" alt="image"
src="https://github.com/user-attachments/assets/5ee16218-34c0-4b8b-9f9b-d33f219760b0"
/>

## 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:

tri.star1011

src/core/game/Game.ts

@@ -171,6 +171,7 @@ export enum GameMapType {
   BajaCalifornia = "Baja California",
   MiddleEast = "Middle East",
   TaiwanStrait = "Taiwan Strait",
+  TheStraits = "The Straits",
 }
 
 export type GameMapName = keyof typeof GameMapType;
@@ -234,6 +235,7 @@ export const mapCategories: Record<string, GameMapType[]> = {
     GameMapType.BajaCalifornia,
     GameMapType.MiddleEast,
     GameMapType.TaiwanStrait,
+    GameMapType.TheStraits,
   ],
   fantasy: [
     GameMapType.Pangaea,