add error/loading/404 boundaries, responsive tables, Metadata API

src/app/[locale]/loading.tsx

@@ -0,0 +1,25 @@
+/**
+ * Loading skeleton for the [locale] segment. Shown during navigation
+ * while a server component fetches (the dashboard, for instance, does
+ * listTenants() + one K8s GET per provisioning row). Textless on
+ * purpose so it needs no translations and adds no layout shift.
+ */
+export default function LocaleLoading() {
+  return (
+    <div className="animate-pulse" aria-hidden="true">
+      <div className="mb-8">
+        <div className="h-7 w-48 rounded-md bg-surface-2" />
+        <div className="mt-4 h-4 w-72 rounded bg-surface-1" />
+      </div>
+      <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-3">
+        {Array.from({ length: 6 }).map((_, i) => (
+          <div
+            key={i}
+            className="h-28 rounded-xl border border-border bg-surface-1"
+          />
+        ))}
+      </div>
+      <span className="sr-only">Loading…</span>
+    </div>
+  );
+}