fix: drawer stays open when moving mouse from rail to drawer

Remove onMouseLeave from individual rail items — only the outer
wrapper handles close. Items only handle onMouseEnter to switch
which drawer is shown. Prevents premature drawer dismissal.

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

frontend/src/components/layout/Sidebar.tsx

@@ -246,13 +246,11 @@ export function Sidebar() {
         key={key}
         className="relative w-full"
         onMouseEnter={() => hasChildren && !sidebarPinned ? openFlyout(key) : undefined}
-        onMouseLeave={() => hasChildren && !sidebarPinned ? closeFlyout() : undefined}
       >
         <Link
           to={item.href}
           onMouseEnter={() => prefetchForRoute(item.href)}
           onFocus={() => hasChildren && !sidebarPinned ? openFlyout(key) : undefined}
-          onBlur={() => hasChildren && !sidebarPinned ? closeFlyout() : undefined}
           className={cn(
             'group relative flex flex-col items-center justify-center rounded-lg px-1 py-2 transition-all duration-150',
             active