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

nuxt.config.ts

@@ -21,7 +21,8 @@ export default defineNuxtConfig({
       firebaseAppId: process.env.NUXT_PUBLIC_FIREBASE_APP_ID,
       firebaseMeasurementId: process.env.NUXT_PUBLIC_FIREBASE_MEASUREMENT_ID,
       stripePublishableKey: process.env.NUXT_PUBLIC_STRIPE_PUBLISHABLE_KEY,
-      backendUrl: process.env.NUXT_PUBLIC_BACKEND_URL || 'http://localhost:3000'
+      backendUrl: process.env.NUXT_PUBLIC_BACKEND_URL || 'http://localhost:3000',
+      storageUrl: process.env.NUXT_PUBLIC_STORAGE_URL || 'http://localhost:9000',
     }
   },
   colorMode: {