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.

.env.example

@@ -0,0 +1,14 @@
+# Auth0 configuration
+AUTH0_DOMAIN=
+AUTH0_CLIENT_ID=
+AUTH0_CLIENT_SECRET=
+AUTH0_AUDIENCE=
+AUTH0_SCOPE=openid profile email
+AUTH0_BASE_URL=http://localhost:3000
+AUTH0_REDIRECT_URI=http://localhost:3000/auth/callback
+
+# Supabase configuration
+SUPABASE_URL=
+SUPABASE_ANON_KEY=
+SUPABASE_SERVICE_ROLE_KEY=
+SUPABASE_STORAGE_BUCKET=designs