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/core/application.cpp

@@ -2089,6 +2089,13 @@ void Application::setupUICallbacks() {
         }
     });
 
+    // Achievement earned callback — show toast banner
+    gameHandler->setAchievementEarnedCallback([this](uint32_t achievementId) {
+        if (uiManager) {
+            uiManager->getGameScreen().triggerAchievementToast(achievementId);
+        }
+    });
+
     // Other player level-up callback — trigger 3D effect + chat notification
     gameHandler->setOtherPlayerLevelUpCallback([this](uint64_t guid, uint32_t newLevel) {
         if (!gameHandler || !renderer) return;