feat(sidebar): update user initials display to show first two letters of first and last name

src/components/Sidebar.jsx

@@ -116,7 +116,7 @@ export default function Sidebar({ open, onClose }) {
                     className="w-full h-full object-cover"
                   />
                 ) : (
-                  (user?.display_name || user?.name)?.[0]?.toUpperCase() || '?'
+                  (user?.display_name || user?.name)?.split(' ').map(n => n[0]).join('').toUpperCase().slice(0, 2) || '?'
                 )}
               </div>
               <div className="min-w-0">