Right-click now attacks hostile NPCs (npcFlags==0) and interacts with
friendly ones in online mode. Parse UNIT_FIELD_FLAGS (59) and
UNIT_NPC_FLAGS (82) from update packets. Stop auto-attack when target
dies or despawns. Add CMSG_ITEM_QUERY_SINGLE/SMSG_ITEM_QUERY_SINGLE_RESPONSE
to populate inventory from server item objects and player slot fields.
- Fix encryption desync by tracking decrypted header bytes in world socket
- Fix UPDATE_OBJECT movement block parsing to handle 3.3.5a update flags
- Fix UNIT_FIELD_DISPLAYID index (67, not 71)
- Add creature spawn/despawn callbacks with DBC-based model loading
- Add SMSG_COMPRESSED_UPDATE_OBJECT opcode support