feat: add design persistence functionality with Auth0 and Supabase integration

- Implemented `useDesignPersistence` composable for managing design records.
- Enhanced `useSlipmatDesigner` to support loading designs from JSON.
- Created global authentication middleware for route protection.
- Added Supabase client plugin for database interactions.
- Developed API endpoints for fetching, saving, and retrieving designs.
- Introduced utility functions for Auth0 token verification and Supabase client retrieval.
- Updated Nuxt configuration to include Auth0 and Supabase environment variables.
- Added necessary dependencies for Auth0 and Supabase.
- Enhanced TypeScript configuration for improved type support.

README.md

@@ -7,17 +7,55 @@ Nuxt 4 single-page experience for creating custom slipmat artwork. Users pick a
 - Template presets for popular vinyl diameters with bleed & safe-zone guides
 - Fabric.js-powered editor: drag, scale, rotate, and stack elements inside a clipped circular canvas
 - Tools for adding text, circles, rectangles, and uploading artwork
-- Live preview card with instant web-resolution snapshot
+- Live preview card with instant web-resolution snapshot and turntable mockup
 - One-click export that produces both preview and print PNGs and offers direct downloads
+- Auth0-protected workspace with Supabase-backed “Save to Library” persistence
 
 ## 🚀 Quick Start
 
 ```bash
+cp .env.example .env   # set Auth0 + Supabase credentials
 npm install
 npm run dev
 ```
 
-Visit [http://localhost:3000](http://localhost:3000) to start designing.
+Visit [http://localhost:3000](http://localhost:3000) to start designing. Authentication is required for every route except the Auth0 callback.
+
+### Auth0 & Supabase configuration
+
+1. **Auth0 application**
+    - Create a SPA application and note the domain, client ID, and client secret.
+    - Add `http://localhost:3000` to the allowed callback, logout, and web origins.
+    - If you plan to call custom APIs, configure an audience and scope (defaults to `openid profile email`).
+
+2. **Supabase project**
+    - Create a storage bucket named `designs` (or change `SUPABASE_STORAGE_BUCKET`).
+    - Create a Postgres table for persisted projects:
+
+       ```sql
+       create table public.designs (
+          id uuid primary key default gen_random_uuid(),
+          user_id text not null,
+          name text not null,
+          template_id text not null,
+          preview_path text not null,
+          preview_url text,
+          design_json jsonb not null,
+          notes text,
+          created_at timestamptz not null default now(),
+          updated_at timestamptz not null default now()
+       );
+
+       create index designs_user_id_updated_at_idx
+          on public.designs (user_id, updated_at desc);
+       ```
+
+    - Grant read/write access to the AUTH0 users via Row Level Security (example policy: `user_id = auth.jwt()->>'sub'`).
+    - Generate an anon key and service role key; place them in `.env` along with the project URL.
+
+3. **Environment**
+    - Populate `.env` using `.env.example` as a guide.
+    - Restart the dev server after changes.
 
 ## 🛠️ Production Builds
 
@@ -37,17 +75,19 @@ Nuxt outputs the server bundle into `.output/`. You can serve it with `node .out
    - _Web preview_: 1024×1024 PNG suitable for the storefront and checkout review.
    - _Print-ready PNG_: Exact template resolution (e.g. 3600×3600 for a 12" slipmat at 300 DPI) for production.
 
-High-res exports remain client-side (no upload yet). Wire the `exportDesign` / `productionBlob` values into your backend to submit orders.
+Saving a project now serializes the Fabric.js canvas, uploads the preview PNG to Supabase Storage, and stores metadata within the `designs` table for quick retrieval.
 
 ## 📦 Tech Stack
 
 - [Nuxt 4](https://nuxt.com/) + Vite
 - [Fabric.js 6](http://fabricjs.com/) for canvas editing
 - Tailwind CSS (via `@tailwindcss/vite`) for styling utilities
+- [Auth0 Vue SDK](https://auth0.com/docs/libraries/auth0-vue) for authentication
+- [Supabase](https://supabase.com/) (Postgres + Storage) for persistence
 
 ## 🧭 Next Ideas
 
-- Persist projects (auth + cloud storage)
+- Project version history and “duplicate design” shortcuts
 - CMYK color profile previews & bleed handling
 - 3D platter preview using Three.js
 - Admin dashboard for incoming print jobs