fix: clear spell visual negative cache on world entry

The spell visual failed-model cache was never cleared across world
changes, so models that failed to load during initial asset loading
(before MPQ/CASC data was fully indexed) would never retry. Now clears
spellVisualFailedModels_ in resetCombatVisualState() alongside the
active spell visual cleanup, giving failed models a fresh attempt on
each world entry.

src/rendering/renderer.cpp

@@ -3023,6 +3023,8 @@ void Renderer::resetCombatVisualState() {
         if (m2Renderer) m2Renderer->removeInstance(sv.instanceId);
     }
     activeSpellVisuals_.clear();
+    // Reset the negative cache so models that failed during asset loading can retry.
+    spellVisualFailedModels_.clear();
 }
 
 bool Renderer::isMoving() const {