v3: lots of small UI tweaks and fixes

src/pages/NotFound.tsx

@@ -0,0 +1,17 @@
+import { Link } from "react-router";
+import { Trans } from "@lingui/react/macro";
+import { PageShell } from "../components/PageShell.tsx";
+
+export function NotFound() {
+  return (
+    <PageShell centered>
+      <h1>404</h1>
+      <p>
+        <Trans>This page does not exist.</Trans>
+      </p>
+      <Link to="/" className="btn-primary">
+        <Trans>Go home</Trans>
+      </Link>
+    </PageShell>
+  );
+}