Rebalance nation configs, they are getting too strong to beat 📊 (#2618)

Resolves #2599

## Description:

For example in #2599 we can see people already struggling with the
higher difficulties.

With my PR #2606 (nation alliance request logic), an alliance request
towards an impossible difficulty nation will probably always get
rejected. They have `maxTroops * 2`, and because humans have much less
troops, the nation of course won't want to ally with them (unless the
human somehow manages to get a similar troop count).

This makes them even harder to beat.

So I tuned the `maxTroops`, `troopIncreaseRate` and `startManpower`
configs towards the setting for humans, following the goal to make
difficulties impact the **SMARTNESS** of nations, instead of just their
troop count configs (more varied gameplay 😊).

The biggest change is in `startManpower`. I thought it was weird that
easy nations started with much less troops than a bot (2_500 vs 10_000).

Look at this screenshot, a couple of seconds into the game. Bots were
bigger than nations. 💀 Turkey in the bottom right corner...

<img width="1536" height="1045" alt="Screenshot 2025-12-14 180823"
src="https://github.com/user-attachments/assets/d219e6ce-b579-4b7e-a8bb-effa339507bf"
/>

## 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/configuration/DefaultConfig.ts

@@ -826,13 +826,13 @@ export class DefaultConfig implements Config {
 
       switch (this._gameConfig.difficulty) {
         case Difficulty.Easy:
-          return 2_500 * strength;
+          return 18_750 * strength;
         case Difficulty.Medium:
-          return 5_000 * strength;
+          return 25_000 * strength; // Like humans
         case Difficulty.Hard:
-          return 20_000 * strength;
+          return 31_250 * strength;
         case Difficulty.Impossible:
-          return 50_000 * strength;
+          return 37_500 * strength;
       }
     }
     return this.infiniteTroops() ? 1_000_000 : 25_000;
@@ -859,13 +859,13 @@ export class DefaultConfig implements Config {
 
     switch (this._gameConfig.difficulty) {
       case Difficulty.Easy:
-        return maxTroops * 0.5;
+        return maxTroops * 0.75;
       case Difficulty.Medium:
-        return maxTroops * 1;
+        return maxTroops * 1; // Like humans
       case Difficulty.Hard:
-        return maxTroops * 1.5;
+        return maxTroops * 1.25;
       case Difficulty.Impossible:
-        return maxTroops * 2;
+        return maxTroops * 1.5;
     }
   }
 
@@ -884,16 +884,16 @@ export class DefaultConfig implements Config {
     if (player.type() === PlayerType.FakeHuman) {
       switch (this._gameConfig.difficulty) {
         case Difficulty.Easy:
-          toAdd *= 0.9;
+          toAdd *= 0.95;
           break;
         case Difficulty.Medium:
-          toAdd *= 1;
+          toAdd *= 1; // Like humans
           break;
         case Difficulty.Hard:
-          toAdd *= 1.1;
+          toAdd *= 1.05;
           break;
         case Difficulty.Impossible:
-          toAdd *= 1.2;
+          toAdd *= 1.1;
           break;
       }
     }