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

app/components/LoginModal.vue

@@ -99,6 +99,17 @@ const handleGoogleLogin = async () => {
           {{ loginError || error }}
         </div>
 
+        <p class="mt-4 text-sm text-slate-400">
+          Need an account?
+          <NuxtLink
+            to="/register"
+            class="text-sky-400 hover:text-sky-300"
+            @click="isOpen = false"
+          >
+            Create one instead
+          </NuxtLink>
+        </p>
+
         <button
           @click="isOpen = false"
           class="mt-4 text-sm text-slate-400 hover:text-white"