- Parse SMSG_DUEL_REQUESTED: store challenger guid/name, set
pendingDuelRequest_ flag, show chat notification
- Parse SMSG_DUEL_COMPLETE: clear pending flag, notify on cancel
- Parse SMSG_DUEL_WINNER: show "X defeated Y in a duel!" chat message
- Handle SMSG_DUEL_OUTOFBOUNDS with warning message
- Add acceptDuel() method sending CMSG_DUEL_ACCEPTED (new builder)
- Wire forfeitDuel() to clear pendingDuelRequest_ on decline
- Add renderDuelRequestPopup() ImGui window (Accept/Decline buttons)
positioned near group invite popup; shown when challenge is pending
- Add DuelAcceptPacket builder to world_packets.hpp/cpp
