feat: parse and display item level and required level in tooltips

- Add itemLevel/requiredLevel fields to ItemQueryResponseData (parsed
  from SMSG_ITEM_QUERY_SINGLE_RESPONSE) and ItemDef
- Propagate through all 5 rebuildOnlineInventory() paths
- Show "Item Level N" and "Requires Level N" in item tooltip in
  standard WoW order (below item name, above required level/stats)

include/game/world_packets.hpp

@@ -1552,6 +1552,8 @@ struct ItemQueryResponseData {
     int32_t intellect = 0;
     int32_t spirit = 0;
     uint32_t sellPrice = 0;
+    uint32_t itemLevel = 0;
+    uint32_t requiredLevel = 0;
     std::string subclassName;
     // Item spells (up to 5)
     struct ItemSpell {