chatgui: proper animation shutdown + TerminateProcess for rlottie threads

- AnimTimer::shutdown(): stop QTimer, clear m_icons before icon destruction
- ~MainWindow: AnimTimer::shutdown() -> cleanupAnimations() (correct order)
- main: replace ExitProcess with TerminateProcess(GetCurrentProcess,0)
  TerminateProcess skips DLL_PROCESS_DETACH, avoiding libwinpthread
  pthread_join hang on rlottie/miniaudio threads.
  rlottie C API has no global shutdown - internal RleTaskScheduler threads
  cannot be stopped through public API. Same for miniaudio WASAPI threads.
  All owned resources already freed before TerminateProcess.

tools/chatgui/src/mainwindow.cpp

@@ -8,6 +8,7 @@
 #include "creategroupdialog.h"
 #include "invite_link.h"
 #include "sound_manager.h"
+#include "animtimer.h"
 #include "../db/db_manager.h"
 #include "../transport/utun_node.h"
 #include "../transport/gui_bridge.h"
@@ -90,6 +91,7 @@ MainWindow::~MainWindow() {
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow — stopping utun node");
     if (m_node) { m_node->stop(); delete m_node; m_node = nullptr; }
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow — node stop+delete done");
+    AnimTimer::shutdown();
     MessageList::cleanupAnimations();
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow — animations cleaned");
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow done");