Implement a "ka-ching" sound effect on kill (#2097)

## Description:
Building off of [this
PR](https://github.com/openfrontio/OpenFrontIO/pull/2090) which
implemented music, I extend this functionality to add sound effects.
Diff will be reduced if and when that PR gets merged!

I think the game would benefit from more sound effects, and adding a
"ka-ching" sound effect on kill seems like an easy place to start.

The ka-ching sound effect was found
[here](https://freesound.org/people/AKkingStudio/sounds/684165/) and is
licensed under Creative Commons.

## 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

Demo video with sound:

https://github.com/user-attachments/assets/18c857a4-a741-492a-bbc1-68d4f3ba38da


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

---------

Co-authored-by: icslucas <carolinacarazolli@gmail.com>

src/client/sound/SoundManager.ts

@@ -1,22 +1,42 @@
-import { Howl, Howler } from "howler";
+import { Howl } from "howler";
 import of4 from "../../../proprietary/sounds/music/of4.mp3";
 import openfront from "../../../proprietary/sounds/music/openfront.mp3";
 import war from "../../../proprietary/sounds/music/war.mp3";
+import kaChingSound from "../../../resources/sounds/effects/ka-ching.mp3";
+
+export enum SoundEffect {
+  KaChing = "ka-ching",
+}
+
 class SoundManager {
   private backgroundMusic: Howl[] = [];
   private currentTrack: number = 0;
+  private soundEffects: Map<SoundEffect, Howl> = new Map();
+  private soundEffectsVolume: number = 1;
+  private backgroundMusicVolume: number = 0;
 
   constructor() {
     this.backgroundMusic = [
-      new Howl({ src: [of4], loop: false, onend: this.playNext.bind(this) }),
+      new Howl({
+        src: [of4],
+        loop: false,
+        onend: this.playNext.bind(this),
+        volume: 0,
+      }),
       new Howl({
         src: [openfront],
         loop: false,
         onend: this.playNext.bind(this),
+        volume: 0,
+      }),
+      new Howl({
+        src: [war],
+        loop: false,
+        onend: this.playNext.bind(this),
+        volume: 0,
       }),
-      new Howl({ src: [war], loop: false, onend: this.playNext.bind(this) }),
     ];
-    this.setBackgroundMusicVolume(0);
+    this.loadSoundEffect(SoundEffect.KaChing, kaChingSound);
   }
 
   public playBackgroundMusic(): void {
@@ -35,14 +55,55 @@ class SoundManager {
   }
 
   public setBackgroundMusicVolume(volume: number): void {
-    const newVolume = Math.max(0, Math.min(1, volume));
-    Howler.volume(newVolume);
+    this.backgroundMusicVolume = Math.max(0, Math.min(1, volume));
+    this.backgroundMusic.forEach((track) => {
+      track.volume(this.backgroundMusicVolume);
+    });
   }
 
   private playNext(): void {
     this.currentTrack = (this.currentTrack + 1) % this.backgroundMusic.length;
     this.playBackgroundMusic();
   }
+
+  public loadSoundEffect(name: SoundEffect, src: string): void {
+    if (!this.soundEffects.has(name)) {
+      const sound = new Howl({
+        src: [src],
+        volume: this.soundEffectsVolume,
+      });
+      this.soundEffects.set(name, sound);
+    }
+  }
+
+  public playSoundEffect(name: SoundEffect): void {
+    const sound = this.soundEffects.get(name);
+    if (sound) {
+      sound.play();
+    }
+  }
+
+  public setSoundEffectsVolume(volume: number): void {
+    this.soundEffectsVolume = Math.max(0, Math.min(1, volume));
+    this.soundEffects.forEach((sound) => {
+      sound.volume(this.soundEffectsVolume);
+    });
+  }
+
+  public stopSoundEffect(name: SoundEffect): void {
+    const sound = this.soundEffects.get(name);
+    if (sound) {
+      sound.stop();
+    }
+  }
+
+  public unloadSoundEffect(name: SoundEffect): void {
+    const sound = this.soundEffects.get(name);
+    if (sound) {
+      sound.unload();
+      this.soundEffects.delete(name);
+    }
+  }
 }
 
 export default new SoundManager();