Add mailbox system and fix logging performance stutter

Implement full mail send/receive: SMSG_SHOW_MAILBOX, CMSG_GET_MAIL_LIST,
SMSG_MAIL_LIST_RESULT, CMSG_SEND_MAIL, SMSG_SEND_MAIL_RESULT, mail take
money/item/delete/mark-as-read, and inbox/compose UI windows.

Fix periodic stuttering in Stormwind caused by synchronous per-line disk
flushes in the logger — remove fileStream.flush() and std::endl, downgrade
high-volume per-packet/per-model/per-texture LOG_INFO to LOG_DEBUG.

include/game/game_handler.hpp

@@ -762,6 +762,23 @@ public:
     bool isVendorWindowOpen() const { return vendorWindowOpen; }
     const ListInventoryData& getVendorItems() const { return currentVendorItems; }
 
+    // Mail
+    bool isMailboxOpen() const { return mailboxOpen_; }
+    const std::vector<MailMessage>& getMailInbox() const { return mailInbox_; }
+    int getSelectedMailIndex() const { return selectedMailIndex_; }
+    void setSelectedMailIndex(int idx) { selectedMailIndex_ = idx; }
+    bool isMailComposeOpen() const { return showMailCompose_; }
+    void openMailCompose() { showMailCompose_ = true; }
+    void closeMailCompose() { showMailCompose_ = false; }
+    void closeMailbox();
+    void sendMail(const std::string& recipient, const std::string& subject,
+                  const std::string& body, uint32_t money, uint32_t cod = 0);
+    void mailTakeMoney(uint32_t mailId);
+    void mailTakeItem(uint32_t mailId, uint32_t itemIndex);
+    void mailDelete(uint32_t mailId);
+    void mailMarkAsRead(uint32_t mailId);
+    void refreshMailList();
+
     // Trainer
     bool isTrainerWindowOpen() const { return trainerWindowOpen_; }
     const TrainerListData& getTrainerSpells() const { return currentTrainerList_; }
@@ -987,6 +1004,12 @@ private:
     void handleArenaTeamEvent(network::Packet& packet);
     void handleArenaError(network::Packet& packet);
 
+    // ---- Mail handlers ----
+    void handleShowMailbox(network::Packet& packet);
+    void handleMailListResult(network::Packet& packet);
+    void handleSendMailResult(network::Packet& packet);
+    void handleReceivedMail(network::Packet& packet);
+
     // ---- Taxi handlers ----
     void handleShowTaxiNodes(network::Packet& packet);
     void handleActivateTaxiReply(network::Packet& packet);
@@ -1322,6 +1345,13 @@ private:
     void startClientTaxiPath(const std::vector<uint32_t>& pathNodes);
     void updateClientTaxi(float deltaTime);
 
+    // Mail
+    bool mailboxOpen_ = false;
+    uint64_t mailboxGuid_ = 0;
+    std::vector<MailMessage> mailInbox_;
+    int selectedMailIndex_ = -1;
+    bool showMailCompose_ = false;
+
     // Vendor
     bool vendorWindowOpen = false;
     ListInventoryData currentVendorItems;

include/game/opcode_table.hpp

@@ -365,6 +365,19 @@ enum class LogicalOpcode : uint16_t {
     CMSG_CHANNEL_LIST,
     SMSG_CHANNEL_LIST,
 
+    // ---- Mail ----
+    SMSG_SHOW_MAILBOX,
+    CMSG_GET_MAIL_LIST,
+    SMSG_MAIL_LIST_RESULT,
+    CMSG_SEND_MAIL,
+    SMSG_SEND_MAIL_RESULT,
+    CMSG_MAIL_TAKE_MONEY,
+    CMSG_MAIL_TAKE_ITEM,
+    CMSG_MAIL_DELETE,
+    CMSG_MAIL_MARK_AS_READ,
+    SMSG_RECEIVED_MAIL,
+    MSG_QUERY_NEXT_MAIL_TIME,
+
     // Sentinel
     COUNT
 };

include/game/world_packets.hpp

@@ -2166,5 +2166,77 @@ public:
     static network::Packet build(uint64_t casterGuid, bool accept);
 };
 
+// ============================================================
+// Mail System
+// ============================================================
+
+struct MailAttachment {
+    uint8_t slot = 0;
+    uint32_t itemGuidLow = 0;
+    uint32_t itemId = 0;
+    uint32_t enchantId = 0;
+    uint32_t randomPropertyId = 0;
+    uint32_t randomSuffix = 0;
+    uint32_t stackCount = 1;
+    uint32_t chargesOrDurability = 0;
+    uint32_t maxDurability = 0;
+};
+
+struct MailMessage {
+    uint32_t messageId = 0;
+    uint8_t messageType = 0;    // 0=normal, 2=auction, 3=creature, 4=gameobject
+    uint64_t senderGuid = 0;
+    uint32_t senderEntry = 0;   // For non-player mail
+    std::string senderName;
+    std::string subject;
+    std::string body;
+    uint32_t stationeryId = 0;
+    uint32_t money = 0;
+    uint32_t cod = 0;           // Cash on delivery
+    uint32_t flags = 0;
+    float expirationTime = 0.0f;
+    uint32_t mailTemplateId = 0;
+    bool read = false;
+    std::vector<MailAttachment> attachments;
+};
+
+/** CMSG_GET_MAIL_LIST packet builder */
+class GetMailListPacket {
+public:
+    static network::Packet build(uint64_t mailboxGuid);
+};
+
+/** CMSG_SEND_MAIL packet builder */
+class SendMailPacket {
+public:
+    static network::Packet build(uint64_t mailboxGuid, const std::string& recipient,
+                                 const std::string& subject, const std::string& body,
+                                 uint32_t money, uint32_t cod);
+};
+
+/** CMSG_MAIL_TAKE_MONEY packet builder */
+class MailTakeMoneyPacket {
+public:
+    static network::Packet build(uint64_t mailboxGuid, uint32_t mailId);
+};
+
+/** CMSG_MAIL_TAKE_ITEM packet builder */
+class MailTakeItemPacket {
+public:
+    static network::Packet build(uint64_t mailboxGuid, uint32_t mailId, uint32_t itemIndex);
+};
+
+/** CMSG_MAIL_DELETE packet builder */
+class MailDeletePacket {
+public:
+    static network::Packet build(uint64_t mailboxGuid, uint32_t mailId, uint32_t mailTemplateId);
+};
+
+/** CMSG_MAIL_MARK_AS_READ packet builder */
+class MailMarkAsReadPacket {
+public:
+    static network::Packet build(uint64_t mailboxGuid, uint32_t mailId);
+};
+
 } // namespace game
 } // namespace wowee

include/ui/game_screen.hpp

@@ -181,6 +181,8 @@ private:
     void renderGuildRoster(game::GameHandler& gameHandler);
     void renderGuildInvitePopup(game::GameHandler& gameHandler);
     void renderChatBubbles(game::GameHandler& gameHandler);
+    void renderMailWindow(game::GameHandler& gameHandler);
+    void renderMailComposeWindow(game::GameHandler& gameHandler);
 
     /**
      * Inventory screen
@@ -242,6 +244,12 @@ private:
     std::vector<ChatBubble> chatBubbles_;
     bool chatBubbleCallbackSet_ = false;
 
+    // Mail compose state
+    char mailRecipientBuffer_[256] = "";
+    char mailSubjectBuffer_[256] = "";
+    char mailBodyBuffer_[2048] = "";
+    int mailComposeMoney_[3] = {0, 0, 0};  // gold, silver, copper
+
     // Left-click targeting: distinguish click from camera drag
     glm::vec2 leftClickPressPos_ = glm::vec2(0.0f);
     bool leftClickWasPress_ = false;