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/empty-state.tsx

@@ -0,0 +1,23 @@
+import { Button } from "@/components/ui/button";
+import { LucideIcon, Plus } from "lucide-react";
+
+interface EmptyStateProps {
+  icon: LucideIcon;
+  title: string;
+  description: string;
+  actionLabel?: string;
+  onAction?: () => void;
+}
+
+export function EmptyState({ icon: Icon, title, description, actionLabel, onAction }: EmptyStateProps) {
+  return (
+    <div className="flex flex-col items-center justify-center py-16 text-center">
+      <div className="rounded-full bg-muted p-4 mb-4"><Icon className="size-8 text-muted-foreground" /></div>
+      <h3 className="text-lg font-semibold">{title}</h3>
+      <p className="text-muted-foreground mt-1 max-w-sm">{description}</p>
+      {actionLabel && onAction && (
+        <Button onClick={onAction} className="mt-4"><Plus className="size-4 mr-2" />{actionLabel}</Button>
+      )}
+    </div>
+  );
+}