refactor: extract loadWeaponM2() to deduplicate weapon model loading

Extract shared M2+skin loading logic into Application::loadWeaponM2(),
replacing duplicate 15-line blocks in loadEquippedWeapons() and
tryAttachCreatureVirtualWeapons(). Future weapon loading changes only
need to update one place.

include/core/application.hpp

@@ -73,6 +73,7 @@ public:
 
     // Weapon loading (called at spawn and on equipment change)
     void loadEquippedWeapons();
+    bool loadWeaponM2(const std::string& m2Path, pipeline::M2Model& outModel);
 
     // Logout to login screen
     void logoutToLogin();