fix: clear lastInteractedGoGuid_ in handleCastFailed path

SMSG_CAST_FAILED is a direct rejection (e.g. insufficient range, no mana)
before the cast starts.  Missing this path meant a stale gather-node guid
could survive into the next timed cast if SMSG_CAST_FAILED fired instead
of SMSG_SPELL_FAILURE.

src/game/game_handler.cpp

@@ -16164,6 +16164,7 @@ void GameHandler::handleCastFailed(network::Packet& packet) {
     castIsChannel = false;
     currentCastSpellId = 0;
     castTimeRemaining = 0.0f;
+    lastInteractedGoGuid_ = 0;
 
     // Stop precast sound — spell failed before completing
     if (auto* renderer = core::Application::getInstance().getRenderer()) {