Add admin login activity logging

- Add AdminLoginLog model to track all login attempts
- Record successful and failed login attempts
- Capture IP address and user agent for each login
- Create /admin/login-logs page to view activity history
- Show login stats (successes, failures, last 30 days)
- Display browser/device and IP for each login
- Add "Login activity" link to admin menu
- Useful for security auditing and monitoring access

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

prisma/schema.prisma

@@ -383,3 +383,13 @@ model OrderItem {
   placementPreviewUrl     String? // front design shown composited on the actual product photo, for reference — where does this go when printing
   placementPreviewUrlBack String? // same, for the back
 }
+
+// Audit log for admin logins — tracks when the admin panel is accessed
+model AdminLoginLog {
+  id        String   @id @default(cuid())
+  loginAt   DateTime @default(now())
+  logoutAt  DateTime? // null = still logged in (or session expired without explicit logout)
+  ipAddress String?
+  userAgent String?
+  success   Boolean  @default(true) // false for failed login attempts
+}