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/layout.tsx

@@ -0,0 +1,16 @@
+import { SettingsSidebar } from "@/components/settings/settings-sidebar";
+
+export default function SettingsLayout({ children }: { children: React.ReactNode }) {
+  return (
+    <div className="max-w-5xl mx-auto">
+      <div className="mb-8">
+        <h1 className="text-3xl font-bold tracking-tight">Settings</h1>
+        <p className="text-muted-foreground mt-1">Manage your account, preferences, and integrations.</p>
+      </div>
+      <div className="flex gap-8 items-start">
+        <SettingsSidebar />
+        <main className="flex-1 min-w-0 space-y-6">{children}</main>
+      </div>
+    </div>
+  );
+}