Add social, collaborative, and gift-registry wishlist capabilities

[Copilot]

This change introduces first-class wishlist sharing and collaboration: public/unlisted links, gift registry workflows, collaborator editing, and social distribution surfaces. It also adds privacy/security controls and analytics so shared wishlists are safe to expose and measurable.

• Backend data model + API surface

  • Added Wishlist, WishlistItem, and WishlistShare models with sharing, collaborator, and registry fields.
  • Added /api/wishlists endpoints for create/list/update/delete, sharing, collaborator management, reserve/purchase/unreserve, registry stats, item comments, and activity feed.
  • Added share-token based public view endpoint and OG image generation endpoint for social previews.

• Registry + collaboration behavior

  • Added reservation/purchase state transitions (reservedBy, reservedUntil, isPurchased, purchasedBy, purchasedAt).
  • Added collaborator edit paths (add/remove collaborators, item add/remove, item comments).
  • Added activity tracking for collaborative updates.

• Security, privacy, and governance

  • Added UUID share token validation and owner-triggered share revocation.
  • Added per-link public view rate limiting.
  • Added reservation cleanup for expired holds.
  • Added public-view redaction behavior (sensitive item fields + optional hidden prices).
  • Added CAPTCHA-token requirement gates for registry actions.
  • Escaped user-controlled values in generated SVG OG image output.

• Frontend wishlist feature set

  • Added WishlistManager, WishlistSettingsModal, ShareWishlist, PublicWishlistView, GiftRegistryView, and CollaborativeWishlist.
  • Added social sharing UX: copy link, QR code (react-qr-code), email share, and Facebook/Twitter/WhatsApp entry points.
  • Added public shared page with Open Graph/Twitter/Pinterest metadata handling and “copy to my wishlist”.
  • Added navigation support for multi-wishlist access, item-count badge, quick-add, and quick list creation.
  • Added frontend/src/api/wishlists.ts client and wired routes in App.tsx.

• Documentation

  • Updated README with wishlist social feature coverage and behavior summary.

// Example: share + public retrieval contract
POST /api/wishlists/:id/share
{
  "userId": "owner-1",
  "shareMethod": "social",
  "expiresAt": "2026-12-31T23:59:59.000Z"
}

GET /api/wishlists/shared/:token
// -> { wishlist: <public-redacted>, shareAnalytics: { totalViews, shareCount } }

Original prompt

Add social and sharing features to wishlists: public URLs, gift registry mode, collaborative wishlists, and social sharing.

Goal: Enable users to share wishlists, create gift registries, and collaborate with others on product lists.

Requirements:

1. Enhanced Data Model:

   interface Wishlist {
     wishlistId: number;
     userId: string;
     name: string;                 // Custom wishlist name
     description?: string;         // Wishlist description
     visibility: 'private' | 'public' | 'unlisted';
     shareToken: string;           // UUID for sharing
     isGiftRegistry: boolean;      // Gift registry mode
     eventDate?: string;           // For gift registries
     collaborators: string[];      // User IDs with edit access
     createdAt: string;
     updatedAt: string;
   }
   
   interface WishlistItem {
     // ... existing fields
     isPurchased: boolean;         // For gift registry
     purchasedBy?: string;         // User ID who bought it
     purchasedAt?: string;         // Purchase timestamp
     reservedBy?: string;          // Temporary reservation
     reservedUntil?: string;       // Reservation expiry
   }
   
   interface WishlistShare {
     shareId: number;
     wishlistId: number;
     shareToken: string;
     sharedBy: string;
     sharedWith?: string;          // Optional recipient
     shareMethod: 'link' | 'email' | 'social';
     createdAt: string;
     expiresAt?: string;
     views: number;
   }

2. Backend API Endpoints:

   • Wishlist Management:

     • POST /api/wishlists - Create named wishlist
     • GET /api/wishlists/:userId - Get user's wishlists
     • PATCH /api/wishlists/:id - Update wishlist settings
     • DELETE /api/wishlists/:id - Delete wishlist

   • Sharing:

     • POST /api/wishlists/:id/share - Generate share link
     • GET /api/wishlists/shared/:token - View shared wishlist (public)
     • POST /api/wishlists/:id/collaborators - Add collaborator
     • DELETE /api/wishlists/:id/collaborators/:userId - Remove collaborator

   • Gift Registry:

     • POST /api/wishlists/:id/items/:itemId/reserve - Reserve item
     • POST /api/wishlists/:id/items/:itemId/purchase - Mark as purchased
     • DELETE /api/wishlists/:id/items/:itemId/unreserve - Cancel reservation
     • GET /api/wishlists/:id/registry-stats - Get purchase status

3. Frontend Components:

   • Components/WishlistManager.tsx:

     • List all user's wishlists
     • Create new wishlist with name/description
     • Switch between wishlists
     • Set default wishlist

   • Components/ShareWishlist.tsx:

     • Generate shareable link (copy to clipboard)
     • QR code for easy sharing
     • Share via email (opens mailto)
     • Share to social media (Facebook, Twitter, WhatsApp)
     • Set expiration date for share links
     • View share analytics (views, clicks)

   • Components/PublicWishlistView.tsx:

     • Public-facing wishlist view (no edit)
     • Show items with prices
     • Hide sensitive info (notes, target prices)
     • "Buy as Gift" buttons (external links)
     • Visitor counter
     • Option to copy list to own wishlist

   • Components/GiftRegistryView.tsx:

     • Show purchased vs available items
     • Reserve item button (24-hour hold)
     • "I bought this" button (marks as purchased)
     • Show who purchased (optional)
     • Progress bar (X of Y items purchased)
     • Thank you message from list owner

   • Components/CollaborativeWishlist.tsx:

     • Add collaborators by email
     • Show who added each item
     • Real-time updates (websocket or polling)
     • Activity feed (X added Y, Z removed W)
     • Collaborator permissions (view/edit)
     • Comments on items

4. Wishlist Settings Modal:

   • Wishlist name and description
   • Visibility toggle (private/public/unlisted)
   • Gift registry mode toggle
   • Event date picker (for registries)
   • Thank you message customization
   • Share link management
   • Collaborator management

5. Navigation Updates:

   • Multiple wishlist selector in nav
   • Badge showing total items across all lists
   • Quick-add to specific wishlist
   • "Create new list" shortcut

6. Social Sharing Integration:

   • Open Graph meta tags for link previews
   • Twitter Card support
   • WhatsApp preview optimization
   • Pinterest Rich Pins
   • Generate og:image with wishlist preview

7. Security & Privacy:

   • Validate share tokens
   • Rate limit public wishlist views
   • Allow owners to revoke share links
   • Hide user emails in public views
   • Option to hide prices in public view
   • CAPTCHA for gift registry actions (prevent abuse)

8. Analytics:

   • Track share method usage
   • Track wishlist views
   • Track items purchased through registry
   • Most shared products
   • Conversion rate (view → purchase)

Technical Notes:

• Generate UUIDs for share tokens (use crypto.randomUUID())
• Implem...