fix: sidebar menu closes on mouseLeave before user can click option

- Remove menu close from onMouseLeave (was closing before user reaches dropdown)
- Add global document click listener to close menu when clicking outside

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

frontend/components/gemini/GeminiSidebar.tsx

@@ -67,6 +67,13 @@ export function GeminiSidebar({
     }
   }, [renamingId]);
 
+  useEffect(() => {
+    if (!menuOpenId) return;
+    const close = () => setMenuOpenId(null);
+    document.addEventListener("click", close);
+    return () => document.removeEventListener("click", close);
+  }, [menuOpenId]);
+
   const handleMenuClick = useCallback((e: React.MouseEvent, convId: string) => {
     e.stopPropagation();
     setMenuOpenId((prev) => (prev === convId ? null : convId));
@@ -150,7 +157,7 @@ export function GeminiSidebar({
                   <button
                     onClick={() => onSelectConversation(conv.id)}
                     onMouseEnter={() => setHoveredId(conv.id)}
-                    onMouseLeave={() => { setHoveredId(null); if (menuOpenId === conv.id) setMenuOpenId(null); }}
+                    onMouseLeave={() => setHoveredId(null)}
                     className={cn(
                       "w-full flex items-center justify-between px-3 py-2.5 rounded-xl text-sm text-left transition-colors duration-150 cursor-pointer group",
                       activeConversationId === conv.id