feat: complete Phase 3 — advanced features for Casera web app

Adds sharing (residence share codes, join, user management, .casera file
export/import), subscription status with feature comparison, notification
preferences with bell icon, profile settings (edit info, change password,
theme picker, delete account), onboarding wizard with create/join paths,
enhanced dashboard with stats cards, Recharts completion chart, recent
activity feed, and task report PDF download.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/(auth)/layout.tsx

@@ -0,0 +1,11 @@
+"use client";
+
+export default function AuthLayout({ children }: { children: React.ReactNode }) {
+  return (
+    <div className="min-h-screen flex items-center justify-center bg-background p-4">
+      <div className="w-full max-w-md">
+        {children}
+      </div>
+    </div>
+  );
+}