feat: homepage animations; Arabic as default locale

apps/web/app/routes/_shared/alternates.ts

@@ -20,7 +20,7 @@
    2. The route's `meta` appends `detailAlternateDescriptors(...)` to whatever
       `buildMeta` produced, which emits <link rel="canonical"> plus one
       <link rel="alternate" hreflang> per locale that actually has a slug, and
-      x-default pointing at English when English exists.
+      x-default pointing at the default locale when it exists.
    3. The route declares `export const handle = SELF_ALTERNATES_HANDLE`, which
       tells the app shell that this page emits its own pair and that the
       shell's prefix-swapped set must be suppressed for it. The shell reads it
@@ -33,7 +33,7 @@
 
 import type { MetaDescriptor } from "react-router";
 
-import { SUPPORTED_LOCALES, type Locale } from "~/i18n/config";
+import { DEFAULT_LOCALE, SUPPORTED_LOCALES, type Locale } from "~/i18n/config";
 import { sectionPath, type RouteSlugKey } from "~/i18n/paths";
 import { canonicalUrl } from "~/lib/seo";
 
@@ -160,8 +160,11 @@ export function detailAlternateDescriptors({
     });
   }
 
-  // x-default is the English URL, because bare "/" negotiates towards English.
-  const fallback = paths.find((entry) => entry.locale === "en");
+  // x-default is the default-locale URL, because bare "/" negotiates towards
+  // the default locale. It must point at an existing page, so a detail page
+  // with no translation yet falls back to whichever locale does exist.
+  const fallback =
+    paths.find((entry) => entry.locale === DEFAULT_LOCALE) ?? paths[0];
   if (fallback) {
     descriptors.push({
       tagName: "link",