game: add area name cache from WorldMapArea.dbc for /who zone display and exploration messages

- Load WorldMapArea.dbc lazily on first use to build areaId→name lookup
- /who results now show [Zone Name] alongside level: 'Name - Level 70 [Stormwind City]'
- SMSG_EXPLORATION_EXPERIENCE now shows 'Discovered Elwynn Forest! Gained X experience.'
  instead of generic 'Discovered new area!' message when the zone name is available
- Cache is populated once per session and shared across both callsites

include/game/game_handler.hpp

@@ -2147,6 +2147,12 @@ private:
     std::unordered_map<uint32_t, std::string> achievementNameCache_;
     bool achievementNameCacheLoaded_ = false;
     void loadAchievementNameCache();
+
+    // Area name cache (lazy-loaded from WorldMapArea.dbc; maps AreaTable ID → display name)
+    std::unordered_map<uint32_t, std::string> areaNameCache_;
+    bool areaNameCacheLoaded_ = false;
+    void loadAreaNameCache();
+    std::string getAreaName(uint32_t areaId) const;
     std::vector<TrainerTab> trainerTabs_;
     void handleTrainerList(network::Packet& packet);
     void loadSpellNameCache();