Locked focus/highlighting option (#387)

## Description:

I've added the option to toggle the Territory highlighting focus from
the current behaviour where the focus set by the currently hovered
player, to "locked focus" which will always focus/highlight your player
territory.

While the highlighting is very helpful to identify your own borders,
especially if you share borders with a player with the same colors, I
find it very distracting, and makes the game feel laggy.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

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

mrh0


![image](https://github.com/user-attachments/assets/aa427233-425d-487e-bfe5-42b390561ab7)

![image](https://github.com/user-attachments/assets/f9a065a3-0fcf-481f-888d-b5781e3717c1)

src/core/game/UserSettings.ts

@@ -24,10 +24,18 @@ export class UserSettings {
     return this.get("settings.leftClickOpensMenu", false);
   }
 
+  focusLocked() {
+    return this.get("settings.focusLocked", false);
+  }
+
   toggleLeftClickOpenMenu() {
     this.set("settings.leftClickOpensMenu", !this.leftClickOpensMenu());
   }
 
+  toggleFocusLocked() {
+    this.set("settings.focusLocked", !this.focusLocked());
+  }
+
   toggleEmojis() {
     this.set("settings.emojis", !this.emojis());
   }