refactor: add isInWorld() and replace 119 inline state+socket checks

Add GameHandler::isInWorld() helper that encapsulates the repeated
'state == IN_WORLD && socket' guard. Replace 99 negative checks and
20 positive checks across game_handler.cpp, plus fix 2 remaining
C-style casts.

include/game/game_handler.hpp

@@ -172,6 +172,7 @@ public:
      * Check if connected to world server
      */
     bool isConnected() const;
+    bool isInWorld() const { return state == WorldState::IN_WORLD && socket; }
 
     /**
      * Get current connection state