verify-agent-os.yml should use inline powershell to avoid checkout

the yaml calls Verify-AgentOS.ps1 which is 21 lines
The script is simple and can be made inline, allowing us to verify agent OS before cloning the repo

Start with verify-agent-os.yml and the 21-line Verify-AgentOS.ps1 script it calls. Compare the workflow's current checkout and verification steps, then confirm the same verification is represented inline before the repository is cloned. Done means the workflow verifies the agent OS without depending on a checkout or the separate script.

Written by the indexing model from the issue text.