replace old client with new client from commafeed-ui repository

commafeed-client/src/components/Loader.tsx

@@ -0,0 +1,9 @@
+import { Center, Loader as MantineLoader } from "@mantine/core"
+
+export function Loader() {
+    return (
+        <Center>
+            <MantineLoader size="xl" variant="bars" />
+        </Center>
+    )
+}