feat(settings): sidebar layout with profile, security, AI, notifications, nutrition

Sticky sidebar nav. Sections: Profile (name/language), Security (email/password change),
AI & Models (BYOK keys + per-use-case model prefs), Notifications (push subscribe),
Nutrition goals. Sub-pages: API keys, Webhooks.

apps/web/app/(app)/settings/notifications/page.tsx

@@ -0,0 +1,20 @@
+import type { Metadata } from "next";
+import { PushSubscribeButton } from "@/components/pwa/push-subscribe-button";
+
+export const metadata: Metadata = { title: "Notifications – Settings" };
+
+export default function NotificationsPage() {
+  return (
+    <div className="space-y-8">
+      <section className="rounded-xl border p-6 space-y-4">
+        <div>
+          <h2 className="font-semibold text-lg">Push Notifications</h2>
+          <p className="text-sm text-muted-foreground mt-1">
+            Get notified when someone comments on your recipes or likes your content.
+          </p>
+        </div>
+        <PushSubscribeButton />
+      </section>
+    </div>
+  );
+}