feat(customers): Add customer detail page with stats and orders

Created comprehensive customer detail page:

Features:
✅ Customer Info Card:
- Avatar with User icon
- Name and email display
- Member/Guest badge
- Stats grid: Total Orders, Total Spent, Registered date

✅ Contact Information:
- Email address
- Phone number (if available)

✅ Billing Address:
- Full address display
- City, state, postcode
- Country

✅ Recent Orders Section:
- Shows last 10 orders
- Order number, status badge, date
- Total amount and item count
- Clickable to view order details
- Link to view all orders

✅ Page Header:
- Customer name as title
- Back button (to customers list)
- Edit button (to edit page)

✅ Navigation:
- Name in index → Detail page (/customers/:id)
- Edit button → Edit page (/customers/:id/edit)
- Order cards → Order detail (/orders/:id)

✅ Loading & Error States:
- Skeleton loaders while fetching
- Error card with retry option
- Empty state for no orders

Technical:
- Uses OrdersApi to fetch customer orders
- Filters completed/processing orders for stats
- Responsive grid layout
- Consistent with other detail pages (Orders)
- TypeScript with proper type annotations

Files:
- Created: routes/Customers/Detail.tsx
- Updated: App.tsx (added route)
- Updated: routes/Customers/index.tsx (links to detail)

Result: Complete customer profile view with order history!

admin-spa/src/App.tsx

@@ -24,6 +24,7 @@ import CouponEdit from '@/routes/Coupons/Edit';
 import CustomersIndex from '@/routes/Customers';
 import CustomerNew from '@/routes/Customers/New';
 import CustomerEdit from '@/routes/Customers/Edit';
+import CustomerDetail from '@/routes/Customers/Detail';
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { LayoutDashboard, ReceiptText, Package, Tag, Users, Settings as SettingsIcon, Maximize2, Minimize2, Loader2 } from 'lucide-react';
 import { Toaster } from 'sonner';
@@ -486,6 +487,7 @@ function AppRoutes() {
       <Route path="/customers" element={<CustomersIndex />} />
       <Route path="/customers/new" element={<CustomerNew />} />
       <Route path="/customers/:id/edit" element={<CustomerEdit />} />
+      <Route path="/customers/:id" element={<CustomerDetail />} />
 
       {/* More */}
       <Route path="/more" element={<MorePage />} />