Added a public game modifier system 😮 For more variety (#2801)

## Description:

Added a public game modifier system. It causes that

5% of public games are played on the compact version of the map
10% of public games have "Random Spawn" activated

Percentages can easily get changed via `DefaultConfig`.
We can also easily add more modifiers.
Modifiers can stack, so in rare cases you will play on a compact map
with random spawn 😄
More variety!

### "Compact Map" modifier implementation

- With the "Compact Map" modifier the lobby max player count gets
reduced to 25% and only 25% of the regular bots and only 25% of the
regular nations will spawn (because the map has only 25% of its regular
size)
- In private lobbies and singleplayer the nation reduction happens too
(When "Compact Map" is enabled).

### Restrictions

- Duos/Trios/Quads team modes do not get Random Spawn (defeats the
purpose)
- Maps with smallest player count < 50 do not get Compact Map in team
games (not enough players after the reduction to 25%). I have calculated
all the possible max player counts.

### How it looks like

Random Spawn modifier:

<img width="528" height="183" alt="Screenshot 2026-01-06 194959"
src="https://github.com/user-attachments/assets/2f729da9-80c3-4548-8205-71129da2a76a"
/>

Very rare case: Two modifiers at the same time and only 10 max players
have been chosen from `[GameMapType.FaroeIslands]: [20, 15, 10]`.
Because of the 75% reduction in player count only 3 players are allowed
(3 is the minimum). I think its funny that you can play a 1v1v1 in rare
occasions 😄

<img width="526" height="184" alt="Screenshot 2026-01-06 194938"
src="https://github.com/user-attachments/assets/834326eb-df03-41b7-b1db-1efa3f1013b5"
/>

### Funny side-effect

Team games with random spawn. That will be interesting. No more "Who is
better in donating troops to the frontline". Instead you have to heavily
coordinate with your teammates.

## 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/core/game/Game.ts

@@ -193,6 +193,11 @@ export enum GameMapSize {
   Normal = "Normal",
 }
 
+export interface PublicGameModifiers {
+  isCompact: boolean;
+  isRandomSpawn: boolean;
+}
+
 export interface UnitInfo {
   cost: (game: Game, player: Player) => Gold;
   // Determines if its owner changes when its tile is conquered.

src/core/game/NationCreation.ts

@@ -2,6 +2,7 @@ import { PseudoRandom } from "../PseudoRandom";
 import { GameStartInfo } from "../Schemas";
 import {
   Cell,
+  GameMapSize,
   GameMode,
   GameType,
   HumansVsNations,
@@ -14,6 +15,7 @@ import { Nation as ManifestNation } from "./TerrainMapLoader";
 /**
  * Creates the nations array for a game, handling HumansVsNations mode specially.
  * In HumansVsNations mode, the number of nations matches the number of human players to ensure fair gameplay.
+ * For compact maps, only 25% of the nations are used.
  */
 export function createNationsForGame(
   gameStart: GameStartInfo,
@@ -31,13 +33,23 @@ export function createNationsForGame(
       new PlayerInfo(n.name, PlayerType.Nation, null, random.nextID()),
     );
 
+  const isCompactMap = gameStart.config.gameMapSize === GameMapSize.Compact;
+
   const isHumansVsNations =
     gameStart.config.gameMode === GameMode.Team &&
     gameStart.config.playerTeams === HumansVsNations;
 
-  // For non-HumansVsNations modes, simply use the manifest nations
+  // For compact maps, use only 25% of nations (minimum 1)
+  let effectiveNations = manifestNations;
+  if (isCompactMap && !isHumansVsNations) {
+    const targetCount = getCompactMapNationCount(manifestNations.length, true);
+    const shuffled = random.shuffleArray(manifestNations);
+    effectiveNations = shuffled.slice(0, targetCount);
+  }
+
+  // For non-HumansVsNations modes, simply use the effective nations
   if (!isHumansVsNations) {
-    return manifestNations.map(toNation);
+    return effectiveNations.map(toNation);
   }
 
   // HumansVsNations mode: balance nation count to match human count
@@ -71,6 +83,20 @@ export function createNationsForGame(
   return nations;
 }
 
+// For compact maps, only 25% of nations are used (minimum 1).
+export function getCompactMapNationCount(
+  manifestNationCount: number,
+  isCompactMap: boolean,
+): number {
+  if (manifestNationCount === 0) {
+    return 0;
+  }
+  if (isCompactMap) {
+    return Math.max(1, Math.floor(manifestNationCount * 0.25));
+  }
+  return manifestNationCount;
+}
+
 const PLURAL_NOUN = Symbol("plural!");
 const NOUN = Symbol("noun!");