feat: parse SMSG_GMTICKET_GETTICKET/SYSTEMSTATUS and SMSG_SPELLINSTAKILLLOG

Previously SMSG_GMTICKET_GETTICKET and SMSG_GMTICKET_SYSTEMSTATUS were
silently consumed. Now both are fully parsed:
- SMSG_GMTICKET_GETTICKET decodes all four status codes (no ticket,
  open ticket, closed, suspended), extracts ticket text, age and
  server-estimated wait time, and stores them on GameHandler.
- SMSG_GMTICKET_SYSTEMSTATUS shows a chat message when GM support
  goes offline/online.
- Added requestGmTicket() (sends CMSG_GMTICKET_GETTICKET) called
  automatically when the GM Ticket UI window is opened, so the player
  sees their existing open ticket text and wait time on first open.
- GM Ticket UI window now shows current-ticket status bar, estimated
  wait time, and hides the Delete button when no ticket is active.

Also implements SMSG_SPELLINSTAKILLLOG (previously silently consumed):
parses caster/victim/spellId for all expansions and emits combat text
when the local player is involved in an instant-kill spell event (e.g.
Execute, Obliterate).

include/ui/game_screen.hpp

@@ -438,7 +438,8 @@ private:
     void  renderEquipSetWindow(game::GameHandler& gameHandler);
 
     // GM Ticket window
-    bool  showGmTicketWindow_ = false;
+    bool  showGmTicketWindow_     = false;
+    bool  gmTicketWindowWasOpen_  = false; ///< Previous frame state; used to fire one-shot query
     char  gmTicketBuf_[2048] = {};
     void  renderGmTicketWindow(game::GameHandler& gameHandler);