TrafficManagement: fix cppcheck constVariablePointer warning

`node` in preloadNextHopsFromNodeDB() is never written through — mark
it const to satisfy cppcheck's constVariablePointer check in CI.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: NomDeTom

src/modules/TrafficManagementModule.cpp

@@ -565,7 +565,7 @@ void TrafficManagementModule::preloadNextHopsFromNodeDB()
     concurrency::LockGuard guard(&cacheLock);
     const size_t count = nodeDB->getNumMeshNodes();
     for (size_t i = 0; i < count; i++) {
-        meshtastic_NodeInfoLite *node = nodeDB->getMeshNodeByIndex(i);
+        const meshtastic_NodeInfoLite *node = nodeDB->getMeshNodeByIndex(i);
         if (!node || node->num == 0 || node->next_hop == 0)
             continue;