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/page-header.tsx

@@ -0,0 +1,28 @@
+"use client";
+import { Button } from "@/components/ui/button";
+import { Plus } from "lucide-react";
+
+interface PageHeaderProps {
+  title: string;
+  description?: string;
+  actionLabel?: string;
+  onAction?: () => void;
+  children?: React.ReactNode;
+}
+
+export function PageHeader({ title, description, actionLabel, onAction, children }: PageHeaderProps) {
+  return (
+    <div className="flex flex-col gap-4 sm:flex-row sm:items-center sm:justify-between">
+      <div>
+        <h1 className="text-2xl font-bold tracking-tight">{title}</h1>
+        {description && <p className="text-muted-foreground mt-1">{description}</p>}
+      </div>
+      <div className="flex items-center gap-2">
+        {children}
+        {actionLabel && onAction && (
+          <Button onClick={onAction}><Plus className="size-4 mr-2" />{actionLabel}</Button>
+        )}
+      </div>
+    </div>
+  );
+}