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/animtimer.cpp

@@ -1,5 +1,6 @@
 #include "animtimer.h"
 #include "lottieicon.h"
+#include "../../lib/debug_config.h"
 
 AnimTimer::AnimTimer() {
     m_timer.setInterval(33);
@@ -12,6 +13,12 @@ AnimTimer *AnimTimer::instance() {
     return &s;
 }
 
+void AnimTimer::shutdown() {
+    instance()->m_timer.stop();
+    instance()->m_icons.clear();
+    DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "AnimTimer: shutdown");
+}
+
 void AnimTimer::registerIcon(const QString &key, LottieIcon *icon) {
     m_icons.insert(key, icon);
 }