fix: correct double-g scroll target to last message element

The double-g press handler was incorrectly scrolling to the first child of the messages container instead of the last element, causing the viewport to jump to the top of the conversation rather than the most recent message. Changed the selector from `.message:first-child` to `lastElementChild` to properly scroll to the latest message before triggering `loadExtra()`.

src/snek/templates/web.html

@@ -227,7 +227,7 @@ document.addEventListener('keydown', function(event) {
         keyTimeout = setTimeout(() => { gPressCount = 0; }, 300);
         if (gPressCount === 2) {
             gPressCount = 0; 
-            messagesContainer.querySelector(".message:first-child")?.scrollIntoView({ block: "end", inline: "nearest" });
+            messagesContainer.lastElementChild?.scrollIntoView({ block: "end", inline: "nearest" });
             loadExtra();
         }
     }