Fix: Add error handling when no orders are generated

[layoutd]

Summary

• Adds error notification when order generation fails due to missing published products
• Makes this failure case more visible than the current "Success: 0 orders generated..." message which can easily be overlooked

Test plan

• Run order generation command with no published products
  wp wc generate orders 10
• Verify clear error message is displayed
  # Error: No orders were generated. Make sure there are published products in your store.
• Run order generation command with 0 requested orders
  wp wc generate orders 0
• No error message since 0 orders was expected.
  # Success: 0 orders generated in 0 seconds
• Add products and then generate orders to see the success message

  wp wc generate products 10
  wp wc generate orders 20
  # Success: 20 orders generated in 3.53 seconds

[Copilot]

Pull Request Overview

This PR adds validation to the order generation CLI command to provide better user feedback when no orders are successfully generated despite a valid request amount.

• Adds a check after order generation to detect when zero orders were created but a positive amount was requested
• Provides an actionable error message directing users to verify published products exist

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