Replace Firebase Storage with MinIO and add user account features

- Storage Integration:
  * Remove Firebase Storage dependency and useFirebaseStorage composable
  * Implement direct MinIO uploads via POST /storage/upload with multipart/form-data
  * Upload canvas JSON, preview PNG, and production PNG as separate objects
  * Store public URLs and metadata in design records

- Authentication & Registration:
  * Add email/password registration page with validation
  * Integrate backend user session via /auth/login endpoint
  * Store backendUser.id as ownerId in design records
  * Auto-sync backend session on Firebase auth state changes

- User Account Pages:
  * Create profile page showing user details and backend session info
  * Create orders page with transaction history filtered by customerEmail
  * Add server proxy /api/orders to forward GET /transactions queries

- Navigation Improvements:
  * Replace inline auth buttons with avatar dropdown menu
  * Add Profile, Orders, and Logout options to dropdown
  * Implement outside-click and route-change handlers for dropdown
  * Display user initials in avatar badge

- API Updates:
  * Update transactions endpoint to accept amount as string
  * Format amount with .toFixed(2) in checkout success flow
  * Query orders by customerEmail instead of ownerId for consistency

.env.example

@@ -3,6 +3,7 @@
 NUXT_PUBLIC_FIREBASE_API_KEY=your_firebase_api_key_here
 NUXT_PUBLIC_FIREBASE_AUTH_DOMAIN=your_firebase_auth_domain_here
 NUXT_PUBLIC_FIREBASE_PROJECT_ID=your_firebase_project_id_here
+# Use the bucket ID (e.g. project-id.appspot.com), not the web URL.
 NUXT_PUBLIC_FIREBASE_STORAGE_BUCKET=your_firebase_storage_bucket_here
 NUXT_PUBLIC_FIREBASE_MESSAGING_SENDER_ID=your_messaging_sender_id_here
 NUXT_PUBLIC_FIREBASE_APP_ID=your_firebase_app_id_here
@@ -14,4 +15,5 @@ STRIPE_SECRET_KEY=sk_test_xxx
 STRIPE_WEBHOOK_SECRET=whsec_xxx
 
 # Backend Configuration
-NUXT_PUBLIC_BACKEND_URL=http://localhost:3000
+NUXT_PUBLIC_BACKEND_URL=http://localhost:3000
+NUXT_PUBLIC_STORAGE_URL=http://localhost:9000