Handle SMSG_ACHIEVEMENT_EARNED with toast banner and chat notification

- Parse SMSG_ACHIEVEMENT_EARNED (guid + achievementId + PackedTime date)
  and fire AchievementEarnedCallback for self, chat notify for others
- Add renderAchievementToast() to GameScreen: slides in from right,
  gold-bordered panel with "Achievement Earned!" title + ID, 5s duration
  with 0.4s slide-in/out animation and fade at end
- Add triggerAchievementToast(uint32_t) public method on GameScreen
- Wire AchievementEarnedCallback in application.cpp
- Add playAchievementAlert() to UiSoundManager, loads
  Sound\Interface\AchievementSound.wav with level-up fallback
- SMSG_ALL_ACHIEVEMENT_DATA silently consumed (no tracker UI yet)

src/audio/ui_sound_manager.cpp

@@ -105,6 +105,13 @@ bool UiSoundManager::initialize(pipeline::AssetManager* assets) {
     levelUpSounds_.resize(1);
     bool levelUpLoaded = loadSound("Sound\\Interface\\LevelUp.wav", levelUpSounds_[0], assets);
 
+    // Load achievement sound (WotLK: Sound\Interface\AchievementSound.wav)
+    achievementSounds_.resize(1);
+    if (!loadSound("Sound\\Interface\\AchievementSound.wav", achievementSounds_[0], assets)) {
+        // Fallback to level-up sound if achievement sound is missing
+        achievementSounds_ = levelUpSounds_;
+    }
+
     // Load error/feedback sounds
     errorSounds_.resize(1);
     loadSound("Sound\\Interface\\Error.wav", errorSounds_[0], assets);
@@ -210,6 +217,9 @@ void UiSoundManager::playDrinking() { playSound(drinkingSounds_); }
 // Level up
 void UiSoundManager::playLevelUp() { playSound(levelUpSounds_); }
 
+// Achievement
+void UiSoundManager::playAchievementAlert() { playSound(achievementSounds_); }
+
 // Error/feedback
 void UiSoundManager::playError() { playSound(errorSounds_); }
 void UiSoundManager::playTargetSelect() { playSound(selectTargetSounds_); }