chatgui: fix all animations showing the same TGS (rlottie model cache key collision)

lottie_animation_from_data uses 'key' as a cache key for parsed models.
All LottieIcon instances were created with key="", causing rlottie's
model cache to return the first loaded animation for all subsequent
requests. Only visible on Windows where rlottie cache is enabled by
default.

Fix: pass unique animPath as key to each LottieIcon constructor.
Also replaced fprintf(stderr) diag with GUI_INFO logging via
AnimTimer::logRegisteredIcons() in debug_ui.h.

tools/chatgui/src/animtimer.cpp

@@ -1,6 +1,6 @@
 #include "animtimer.h"
 #include "lottieicon.h"
-#include "../../lib/debug_config.h"
+#include "debug_ui.h"
 
 AnimTimer::AnimTimer() {
     m_timer.setInterval(33);
@@ -49,3 +49,13 @@ void AnimTimer::onTimer() {
         icon->advanceFrame();
     emit ticked();
 }
+
+void AnimTimer::logRegisteredIcons() const {
+    for (auto it = m_icons.constBegin(); it != m_icons.constEnd(); ++it) {
+        LottieIcon *icon = it.value();
+        GUI_INFO("LottieIcon: path=%s frames=%d size=%dx%d tgsSize=%d valid=%d",
+                 qPrintable(it.key()), icon->frameCount(),
+                 icon->originalSize().width(), icon->originalSize().height(),
+                 icon->tgsSize(), (int)icon->isValid());
+    }
+}