feat(mastermind): improve UI layout and enhance peg reveal animation

- Relocate Leave button to the bottom of the game screen
- Extend peg reveal animation duration to 2.3s with smoother tick timing
- Introduce MASTERMIND_CALCULATE sound effect to play during the reveal
- Update audio preload and SFX registry to support the new sound

public/src/games/mastermind/MastermindGame.js

@@ -88,7 +88,7 @@ export default class MastermindGame extends Phaser.Scene {
     this.rightLayer   = this.add.container(0, 0).setDepth(DEPTH.rows);
     this.composeLayer = this.add.container(0, 0).setDepth(DEPTH.compose);
 
-    new Button(this, GAME_WIDTH - 120, 60, 'Leave', () => this.scene.start('GameMenu'), {
+    new Button(this, GAME_WIDTH - 120, GAME_HEIGHT - 60, 'Leave', () => this.scene.start('GameMenu'), {
       variant: 'ghost', width: 160, height: 46, fontSize: 20,
     }).setDepth(DEPTH.ui);
 
@@ -596,10 +596,14 @@ export default class MastermindGame extends Phaser.Scene {
       this.fxLayer.add(peg);
       pegsObjs.push(peg);
     }
+    // 2.3 seconds total: 32 ticks at ~72ms each
+    const totalDuration = 2300;
+    const tickInterval = totalDuration / 32;
+    playSound(this, SFX.MASTERMIND_CALCULATE);
     let ticks = 0;
-    const maxTicks = 9;
+    const maxTicks = 32;
     const ev = this.time.addEvent({
-      delay: 70, repeat: maxTicks,
+      delay: tickInterval, repeat: maxTicks,
       callback: () => {
         ticks++;
         pegsObjs.forEach((p, c) => {

public/src/scenes/PreloadScene.js

@@ -69,6 +69,7 @@ export default class PreloadScene extends Phaser.Scene {
     this.load.audio('sfx-mastermind-access-denied', '/assets/fx/mastermind-access-denied.mp3');
     this.load.audio('sfx-mastermind-color', '/assets/fx/mastermind-color.mp3');
     this.load.audio('sfx-mastermind-match', '/assets/fx/mastermind-match.mp3');
+    this.load.audio('sfx-mastermind-calculate', '/assets/fx/mastermind-calculate.mp3');
     this.load.audio('sfx-roulette', '/assets/fx/roulette.mp3');
     this.load.audio('sfx-battleship-hit', '/assets/fx/battleship-hit.mp3');
     this.load.audio('sfx-battleship-miss', '/assets/fx/battleship-miss.mp3');

public/src/ui/Sounds.js

@@ -24,7 +24,8 @@ export const SFX = {
   MASTERMIND_GRANTED:  'sfx-mastermind-access-granted',
   MASTERMIND_DENIED:   'sfx-mastermind-access-denied',
   MASTERMIND_COLOR:    'sfx-mastermind-color',
-  MASTERMIND_MATCH:    'sfx-mastermind-match',
+  MASTERMIND_MATCH:      'sfx-mastermind-match',
+  MASTERMIND_CALCULATE:  'sfx-mastermind-calculate',
 };
 
 export function playSound(scene, key) {