add 404 error page

apps/client/src/components/ui/error-404.tsx

@@ -0,0 +1,19 @@
+import { Title, Text, Button, Container, Group } from "@mantine/core";
+import classes from "./error-404.module.css";
+import { Link } from "react-router-dom";
+
+export function Error404() {
+  return (
+    <Container className={classes.root}>
+      <Title className={classes.title}>404 Page Not Found</Title>
+      <Text c="dimmed" size="lg" ta="center" className={classes.description}>
+        Sorry, we can't find the page you are looking for.
+      </Text>
+      <Group justify="center">
+        <Button component={Link} to={"/home"} variant="subtle" size="md">
+          Take me back to homepage
+        </Button>
+      </Group>
+    </Container>
+  );
+}