add 404 page

src/pages/404.tsx

@@ -0,0 +1,22 @@
+import Container from 'components/Container';
+import React, { useContext, useEffect, useState } from 'react';
+import constants from 'utils/strings/constants';
+import { AppContext } from './_app';
+
+export default function NotFound() {
+    const appContext = useContext(AppContext);
+    const [loading, setLoading] = useState(true);
+    useEffect(() => {
+        appContext.showNavBar(true);
+        setLoading(false);
+    }, []);
+    return (
+        <Container>
+            {loading ? (
+                <span className="sr-only">Loading...</span>
+            ) : (
+                constants.NOT_FOUND
+            )}
+        </Container>
+    );
+}

src/utils/strings/englishConstants.tsx

@@ -623,6 +623,7 @@ const englishConstants = {
     CUSTOM_TIME: 'custom time',
     REOPEN_PLAN_SELECTOR_MODAL: 're-open plans',
     OPEN_PLAN_SELECTOR_MODAL_FAILED: 'failed to open plans',
+    NOT_FOUND: '404 not found',
 };
 
 export default englishConstants;