Fix nations being blocked by PVP immunity 🛡️ (#4282)

## Description:

### Problem

PVP immunity (the extended spawn immunity setting) was incorrectly
preventing AI nations from attacking human players. The intent of PVP
immunity is to protect human-vs-human combat only, but nations were
subject to the same restriction.

### Root Cause

In `canAttackPlayer()`, only `PlayerType.Bot` was exempt from checking
target immunity. Nations fell through to the same path as humans, so
when a nation tried to attack an immune human, `player.isImmune()`
returned true and the attack was blocked.

### Fix

Changed the immunity bypass condition from `this.type() ===
PlayerType.Bot` to `this.type() !== PlayerType.Human`. Now only human
attackers check target immunity. Both bots and nations bypass it (they
only check alliance status).

This does not affect nation spawn immunity
(`nationSpawnImmunityDuration`), which is a separate mechanism that
protects newly spawned nations from all attackers and continues to work
independently.

## 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

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

FloPinguin

src/core/game/PlayerImpl.ts

@@ -1608,11 +1608,10 @@ export class PlayerImpl implements Player {
     player: Player,
     treatAFKFriendly: boolean = false,
   ): boolean {
-    if (this.type() === PlayerType.Bot) {
-      // Bots are not affected by immunity
+    if (this.type() !== PlayerType.Human) {
+      // Only human attackers respect PVP immunity
       return !this.isFriendly(player, treatAFKFriendly);
     }
-    // Humans and Nations respect immunity
     return !player.isImmune() && !this.isFriendly(player, treatAFKFriendly);
   }