chatgui: fix Ctrl-C on Linux — remove thread_local from g_currentNode

SIGINT on Linux can be delivered to any thread (not just worker).
signal_handler uses g_currentNode->requestStop(); with thread_local,
g_currentNode was nullptr in non-worker threads — Ctrl-C did nothing.

Removing thread_local fixes signal delivery: g_currentNode is set once
before signal handler is registered, pointer read is atomic on x86/x64.

tools/chatgui/transport/utun_node.cpp

@@ -33,7 +33,7 @@ extern "C" {
 
 #define ETCP_RT_ID_CHAT  0x11
 
-static thread_local UtunNode* g_currentNode = nullptr;
+static UtunNode* g_currentNode = nullptr;
 
 static void signal_handler(int sig) {
     (void)sig;