Clarify do-not-create-organization warning for Copilot Business standalone setup

The previous warning was a single unbolded paragraph buried under the trial
button. Customers setting up a dedicated enterprise account for Copilot
Business were missing it, creating an organization during the trial flow,
and getting billed for GitHub Enterprise licenses they did not need.

Changes:
- Promote the warning to a [!WARNING] callout so it visually stands out
- State the explicit goal-state (0 seats of GitHub Enterprise)
- Add the consequence (billing for GitHub Enterprise) so readers understand
  the cost impact, not just the policy
- Tell the reader what to do instead (add users directly to the enterprise)
- Add one line calling out that this path is correct for ADO-only / non-
  GitHub-hosted code customers, which is the most common scenario for
  Copilot Business standalone

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mattstana

content/copilot/how-tos/copilot-on-github/set-up-copilot/enable-copilot/set-up-a-dedicated-enterprise-for-copilot-business.md

@@ -29,7 +29,14 @@ Start a trial of {% data variables.product.prodname_ghe_cloud %} to create your
 
 <a href="https://github.com/account/enterprises/new?ref_product=ghec&ref_type=trial&ref_style=button&ref_plan=enterprise" target="_blank" class="btn btn-primary mt-3 mr-3 no-underline"><span>Set up a trial of {% data variables.product.prodname_ghe_cloud %}</span> {% octicon "link-external" height:16 aria-label="link-external" %}</a>
 
-Do not create any organizations during setup. Adding users to organizations assigns {% data variables.product.prodname_enterprise %} licenses, while adding users directly to the enterprise keeps your setup limited to {% data variables.copilot.copilot_business_short %}.
+> [!WARNING]
+> **Do not create an organization during setup.** This enterprise account exists only as a billing and identity container for {% data variables.copilot.copilot_business_short %} licenses - it should have **0 seats of {% data variables.product.prodname_enterprise %}** when you are done.
+>
+> Creating an organization, or adding users to an organization later, will assign {% data variables.product.prodname_enterprise %} licenses and bill your account for {% data variables.product.prodname_enterprise %} - which you do not need for {% data variables.copilot.copilot_business_short %}.
+>
+> Instead, add users **directly to the enterprise** (see the next section). They will receive {% data variables.copilot.copilot_business_short %} licenses without any {% data variables.product.prodname_enterprise %} cost.
+
+This setup is also the recommended path for customers whose code lives outside of {% data variables.product.github %} (for example, on Azure DevOps) and who only want {% data variables.copilot.copilot_business_short %} in the IDE.
 
 ## Add users to your enterprise