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)

include/ui/game_screen.hpp

@@ -326,8 +326,15 @@ private:
     uint32_t dingLevel_ = 0;
     void renderDingEffect();
 
+    // Achievement toast banner
+    static constexpr float ACHIEVEMENT_TOAST_DURATION = 5.0f;
+    float achievementToastTimer_ = 0.0f;
+    uint32_t achievementToastId_ = 0;
+    void renderAchievementToast();
+
 public:
     void triggerDing(uint32_t newLevel);
+    void triggerAchievementToast(uint32_t achievementId);
 };
 
 } // namespace ui