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

server/api/designs/[designId].get.ts

@@ -0,0 +1,30 @@
+export default defineEventHandler(async (event) => {
+  const params = event.context.params as { designId?: string }
+  const designId = params?.designId
+
+  if (!designId) {
+    throw createError({ statusCode: 400, statusMessage: "Missing design id" })
+  }
+
+  const config = useRuntimeConfig()
+  const backendUrl = config.public?.backendUrl
+
+  if (!backendUrl) {
+    throw createError({ statusCode: 500, statusMessage: "Backend URL not configured" })
+  }
+
+  try {
+    const design = await $fetch(`/designs/${encodeURIComponent(designId)}`, {
+      baseURL: backendUrl,
+      method: "GET",
+    })
+
+    return design
+  } catch (err) {
+    console.error(`[designs] Failed to fetch design ${designId}`, err)
+    throw createError({
+      statusCode: 502,
+      statusMessage: (err as Error)?.message ?? "Failed to load design",
+    })
+  }
+})