enhance dashboard and user interface: update heading sizes, translate user label to German, and implement loan management features including fetching and displaying loans with error handling

admin/src/Layout/Dashboard.tsx

@@ -36,7 +36,7 @@ const Dashboard: React.FC<DashboardProps> = ({ onLogout }) => {
           borderColor="gray.200"
           bg="gray.900"
         >
-          <Heading size="md">Dashboard</Heading>
+          <Heading size="xl">Dashboard</Heading>
           <Flex align="center" gap={6}>
             <Text fontSize="sm" color="white">
               Willkommen {userName}, im Admin-Dashboard!

admin/src/Layout/Sidebar.tsx

@@ -39,7 +39,7 @@ const Sidebar: React.FC<SidebarProps> = ({
             _hover={{ bg: "gray.700", textDecoration: "none" }}
             onClick={viewUser}
           >
-            User
+            Benutzer
           </Link>
           <Link
             px={3}