Handle Nation win condition (#2824)

Resolves #2823

## Description:

When playing in single-player mode, if an NPC reaches 80% land control
before the player, the game enters a broken state where:

- The game clock stops
- Win checking stops permanently
- Even if the player later conquers 100% of land, victory is never
awarded
- The game becomes "stuck" in a zombie state.

This PR addresses this allowing Nations to be set as winners in single
mode, and in this case showing a "Nation {nation} has won" modal to the
user. This WinModal is the same as the "{player} has won", with the only
change being the title.

Nation wins in FFA, from the human player perspective:

<img width="1457" height="837" alt="image"
src="https://github.com/user-attachments/assets/1ce569bd-6616-4a23-b4a4-afedad2c64f8"
/>

## 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:

deshack_82603

src/client/graphics/layers/WinModal.ts

@@ -303,6 +303,12 @@ export class WinModal extends LitElement implements Layer {
           this.isWin = false;
         }
         this.show();
+      } else if (wu.winner[0] === "nation") {
+        this._title = translateText("win_modal.nation_won", {
+          nation: wu.winner[1],
+        });
+        this.isWin = false;
+        this.show();
       } else {
         const winner = this.game.playerByClientID(wu.winner[1]);
         if (!winner?.isPlayer()) return;

src/core/Schemas.ts

@@ -472,6 +472,7 @@ export const WinnerSchema = z
   .union([
     z.tuple([z.literal("player"), ID]).rest(ID),
     z.tuple([z.literal("team"), SafeString]).rest(ID),
+    z.tuple([z.literal("nation"), SafeString]).rest(ID),
   ])
   .optional();
 export type Winner = z.infer<typeof WinnerSchema>;

src/core/game/GameImpl.ts

@@ -718,7 +718,9 @@ export class GameImpl implements Game {
       ];
     } else {
       const clientId = winner.clientID();
-      if (clientId === null) return;
+      if (clientId === null) {
+        return ["nation", winner.name()];
+      }
       return [
         "player",
         clientId,