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/components/shared/error-banner.tsx

@@ -0,0 +1,18 @@
+"use client";
+import { Button } from "@/components/ui/button";
+import { AlertTriangle } from "lucide-react";
+
+interface ErrorBannerProps {
+  message?: string;
+  onRetry?: () => void;
+}
+
+export function ErrorBanner({ message = "Something went wrong. Please try again.", onRetry }: ErrorBannerProps) {
+  return (
+    <div className="rounded-lg border border-destructive/50 bg-destructive/10 p-4 flex items-center gap-3">
+      <AlertTriangle className="size-5 text-destructive shrink-0" />
+      <p className="text-sm text-destructive flex-1">{message}</p>
+      {onRetry && <Button variant="outline" size="sm" onClick={onRetry}>Retry</Button>}
+    </div>
+  );
+}