Implement basic trade request/accept/decline flow

- Parse SMSG_TRADE_STATUS for all 20+ status codes: incoming request,
  open/cancel/complete/accept notifications, error conditions (too far,
  wrong faction, stunned, dead, trial account, etc.)
- SMSG_TRADE_STATUS_EXTENDED consumed via shared handler (no full item
  window yet; state tracking sufficient for accept/decline flow)
- Add acceptTradeRequest() (CMSG_BEGIN_TRADE), declineTradeRequest(),
  acceptTrade() (CMSG_ACCEPT_TRADE), cancelTrade() (CMSG_CANCEL_TRADE)
- Add BeginTradePacket, CancelTradePacket, AcceptTradePacket builders
- Add renderTradeRequestPopup(): shows "X wants to trade" with
  Accept/Decline buttons when tradeStatus_ == PendingIncoming
- TradeStatus enum tracks None/PendingIncoming/Open/Accepted/Complete

include/game/game_handler.hpp

@@ -707,6 +707,18 @@ public:
     bool hasPendingGroupInvite() const { return pendingGroupInvite; }
     const std::string& getPendingInviterName() const { return pendingInviterName; }
 
+    // ---- Trade ----
+    enum class TradeStatus : uint8_t {
+        None = 0, PendingIncoming, Open, Accepted, Complete
+    };
+    TradeStatus getTradeStatus() const { return tradeStatus_; }
+    bool hasPendingTradeRequest() const { return tradeStatus_ == TradeStatus::PendingIncoming; }
+    const std::string& getTradePeerName() const { return tradePeerName_; }
+    void acceptTradeRequest();   // respond to incoming SMSG_TRADE_STATUS(1) with CMSG_BEGIN_TRADE
+    void declineTradeRequest();  // respond with CMSG_CANCEL_TRADE
+    void acceptTrade();          // lock in offer: CMSG_ACCEPT_TRADE
+    void cancelTrade();          // CMSG_CANCEL_TRADE
+
     // ---- Duel ----
     bool hasPendingDuelRequest() const { return pendingDuelRequest_; }
     const std::string& getDuelChallengerName() const { return duelChallengerName_; }
@@ -1268,6 +1280,7 @@ private:
 
     // ---- Instance lockout handler ----
     void handleRaidInstanceInfo(network::Packet& packet);
+    void handleTradeStatus(network::Packet& packet);
     void handleDuelRequested(network::Packet& packet);
     void handleDuelComplete(network::Packet& packet);
     void handleDuelWinner(network::Packet& packet);
@@ -1625,6 +1638,11 @@ private:
     bool pendingGroupInvite = false;
     std::string pendingInviterName;
 
+    // Trade state
+    TradeStatus tradeStatus_  = TradeStatus::None;
+    uint64_t    tradePeerGuid_= 0;
+    std::string tradePeerName_;
+
     // Duel state
     bool pendingDuelRequest_    = false;
     uint64_t duelChallengerGuid_= 0;

include/game/world_packets.hpp

@@ -1326,6 +1326,24 @@ public:
     static network::Packet build(uint64_t targetGuid);
 };
 
+/** CMSG_BEGIN_TRADE packet builder (no payload — accepts incoming trade request) */
+class BeginTradePacket {
+public:
+    static network::Packet build();
+};
+
+/** CMSG_CANCEL_TRADE packet builder (no payload) */
+class CancelTradePacket {
+public:
+    static network::Packet build();
+};
+
+/** CMSG_ACCEPT_TRADE packet builder (no payload — lock in current offer) */
+class AcceptTradePacket {
+public:
+    static network::Packet build();
+};
+
 /** CMSG_ATTACKSWING packet builder */
 class AttackSwingPacket {
 public: