web/settings: redirect invalid settings paths to default settings page

web/src/lib/settings/defaults.ts

@@ -1,3 +1,4 @@
+import { browser } from "$app/environment";
 import { defaultLocale } from "$lib/i18n/translations";
 import type { CobaltSettings } from "$lib/types/settings";
 
@@ -35,4 +36,15 @@ const defaultSettings: CobaltSettings = {
     },
 }
 
+const defaultSettingsPage = () => {
+    if (browser) {
+        if (window.innerWidth <= 750) {
+            return "/settings";
+        }
+    }
+
+    return "/settings/general/appearance";
+}
+
 export default defaultSettings;
+export { defaultSettingsPage };

web/src/routes/+error.svelte

@@ -0,0 +1,17 @@
+<script lang="ts">
+	import { goto } from '$app/navigation';
+	import { page } from '$app/stores';
+	import { defaultSettingsPage } from '$lib/settings/defaults';
+
+	$: {
+		if (
+			$page.error?.message === 'Not Found'
+			&& $page.url.pathname.startsWith('/settings')
+		) {
+			goto(defaultSettingsPage(), { replaceState: true });
+		}
+	}
+</script>
+
+<!-- TODO: nicer errors -->
+<h1>{$page.status}: {$page.error?.message}</h1>